March 2014: I do more and more of my research online, and I organize those sources on this Pinterest board : 
Marine Biology:
The Naturalist's Guide to the Atlantic Seashore: Beach Ecology from the Gulf of Maine to Cape Hatteras, Scott Wesley Shumway, 2008. If I had to pick one book to recommend, this would be it. Great pictures, comprehensive explanations of various tidal ecosystems. This is the one that answered the barnacles-and-mussels question. Not great for identification, though.
 Eastern Tidepool & Reef: North-Central Atlantic Marinelife Guide, Dr. C. Harvey-Clark, 1997. A slim paperback with good clear color photographs (small ones, to fit the scale of the book) and very short paragraphs of information about each creature.
 
Life Between the Tides: Marine Plants and Animals of the Northeast, Watling, Fegley & Moring, 2003. Similar to the book above, with black-and-white drawings instead of photos. Well-written and informative, but not one of my favorites for identification.
Life Between the Tides: Marine Plants and Animals of the Northeast, Watling, Fegley & Moring, 2003. Similar to the book above, with black-and-white drawings instead of photos. Well-written and informative, but not one of my favorites for identification.
These next few are old books I found at library sales over the years and have found useful:
SeaBeach at Ebb Tide ,  Augusta Foote Arnold, 1901. The seaweed and barnacle photos are not  clear enough to help identify most specimens. The engravings of crabs,  on the other hand, are fantastic.
,  Augusta Foote Arnold, 1901. The seaweed and barnacle photos are not  clear enough to help identify most specimens. The engravings of crabs,  on the other hand, are fantastic.
Beginner's Guide to Seashore Life , Leon Hausman, 1949. Very helpful in identifying common seaweed and crustaceans.
, Leon Hausman, 1949. Very helpful in identifying common seaweed and crustaceans.
The Biology of the Sea-Shore ,  Flattely & Walton, 1922. Not intended for identification of  specimens, this one has chapter headings like "The Accommodation of  Water-breathers to Breathing in Air," The Effects of Varying Salinity,"  and "Reciprocal Adaptation on the Part of Foes." Best for the  beachcomber equally obsessed with marine biology and old books.
,  Flattely & Walton, 1922. Not intended for identification of  specimens, this one has chapter headings like "The Accommodation of  Water-breathers to Breathing in Air," The Effects of Varying Salinity,"  and "Reciprocal Adaptation on the Part of Foes." Best for the  beachcomber equally obsessed with marine biology and old books.
Science on the Shores and Banks ,  Elizabeth Cooper, 1960. Written for intelligent, literate children,  this one is of interest for adults, too. She  discusses both salt- and freshwater shorelines.
,  Elizabeth Cooper, 1960. Written for intelligent, literate children,  this one is of interest for adults, too. She  discusses both salt- and freshwater shorelines.
From Cape Cod to the Bay of Fundy: An Environmental Atlas for the Gulf of Maine, ed. Philip Conkling, 1995. A series of essays by a variety of scientists studying the Gulf, this book has some very good satellite images and diagrams of ocean currents. It is not particularly readable and took an effort of will to finish, but I learned a lot about my piece of the Atlantic, most notably that it is barely connected to the Atlantic! If you live in the Gulf of Maine area, are strong-willed or obsessively curious, and you run across this in a used bookshop for a reasonable price, by all means get it.
Seaweeds, C.J. Hillson, 1982. "A Color-Coded, Illustrated Guide to Common Marine Plants of the East Coast of the United States." I borrowed this one from the College of the Atlantic library, and it doesn't seem to be available online. It is illustrated with very clear line drawings and has basic information on seaweed from the entire East Coast. It is a little too general for my needs, since it includes a lot of warm-water algae, but a good back-up.
Marine Algae of the Northeastern Coast of North America, William Randolph Taylor, 1962. This one also came from the College library, and phew! it is a serious textbook, 509 pages of marine algae. Great line drawings, very clear and useful for identification. [10/31/12: This one was so useful I bought my own copy.]
Artificial Key to the Common Marine Algae of New England North of Cape Cod, Lamb, Zimmermann & Webber, 1977. Yes, another one from the College library. A slim pamphlet of 53 pages with some of the best drawings, an excellent resource. I would pick it up for my own library in a heartbeat: found it on Amazon for $110. Sheesh.
Beachcombing:
 Pure Sea Glass, Richard LaMotte, 2004.  The  bible of sea glass. Really. Everything from comparative photos of  different bottle tops with the dates they were in use to an explanation  of how manganese turns clear glass purple when exposed to UV light. If  you don't care about crustaceans and seaweed and you are just in it for  the sea glass, forget the book above, this is the one you want.
The  bible of sea glass. Really. Everything from comparative photos of  different bottle tops with the dates they were in use to an explanation  of how manganese turns clear glass purple when exposed to UV light. If  you don't care about crustaceans and seaweed and you are just in it for  the sea glass, forget the book above, this is the one you want. 
 
Sea Glass Chronicles, C.S Lambert, 2001. A larger-format art book, this one has pretty photos accompanied with snippets of information. Not a reference volume, but I did learn a few new details about pottery.
Sea Glass Chronicles, C.S Lambert, 2001. A larger-format art book, this one has pretty photos accompanied with snippets of information. Not a reference volume, but I did learn a few new details about pottery.
The Art of Shelling, Chuck & Debbie Robinson, 2008. A  very useful little book. I actually read about a beach (sort-of) near  me in this book, tracked it down, and had a lovely afternoon. More  focused on the southern part of the country (remember I am in Maine, so  southern is New Hampshire and beyond.) Good advice on collecting and  cleaning shells. Hmm, I should re-read this one, it has been a while!
The Sea Glass Artists website. This  is a great place to ask questions about things you find. You can post  photos in the forums and knowledgeable beachcombers from all over the  world will tell you what they think it is. There are also fantastic  photos of the amazing things (not just glass) that people have found.  Cameos, marbles, a French railroad watch, antique binoculars, and  mystery objects galore. And of course, glass. Lots and lots of sea  glass. Who knew there was so much out there?!
 
Flotsametrics, Curtis Ebbesmeyer, 2009. How   trash moves through the oceans of the world and ends up on your beach.   An appealing mixture of hard science and colloquial story-telling, and an excellent introduction to the world of ocean currents. The   rare book that is both entertaining and informative. Highly  recommended!
 
Washed Up, Skye Moody, 2006. A chatty and informative look at a wide range of flotsam. Glass balls, shipwrecks, sea beans and so forth. Some of this is covered in Flotsametrics, some was new to me. The author's somewhat coy sense of humor grated on me, but the book was interesting enough that I stuck with it. You might find her amusing; humor is so personal.
Washed Up, Skye Moody, 2006. A chatty and informative look at a wide range of flotsam. Glass balls, shipwrecks, sea beans and so forth. Some of this is covered in Flotsametrics, some was new to me. The author's somewhat coy sense of humor grated on me, but the book was interesting enough that I stuck with it. You might find her amusing; humor is so personal.
Other interesting resources:
USGS Bedrock Maps
I  usually associate the USGS with the incredibly useful topographic maps  they issue, completely forgetting that it is, after all the US  Geological Survey. Forgetting, that is, until I get curious about what I  am walking on, and then I go poke around on their website looking for  local geology maps.
 
Roadside Geology of Maine, D.W. Caldwell, 2007. This is a great book for the insatiably curious. It is organized like a travel guidebook, discussing the geological formation visible from roads throughout the state. It appears to be part of a series - there are similarly titled books for several other states. Like Fodor's for people with rocks in their heads!
 
Ice, Mariana Gosnell, 2007.  Fascinating,  well-written book on every aspect of ice that I can imagine. Includes 2  chapters on sea ice. Worth reading just for the first chapter, a long  and incredibly detailed description of watching a lake freeze in New  England. I know, sounds like as much fun as watching paint dry, and it  takes longer, but really, she's a good writer and it is fascinating  stuff.
 
The Wave, Susan Casey, 2010. All about gigantic waves, the ships they have crushed, and the surfers who ride them. Entertaining and interesting.
 
Living with the Coast of Maine, Kelley, Kelley & Pilkey, 1989. Some chapter titles: "Where does beach sand come from," "What can I do about my eroding beach," "Shoreline engineering: stabilizing the unstable," "Selecting a site on the Maine coast," "Coastal land use and the law in Maine," "Coastal forces: design requirements," "Building or buying a house near the beach." You get the idea. An incredibly useful and practical book about erosion, coastal dynamics, and building near the ocean.
Living with the Coast of Maine, Kelley, Kelley & Pilkey, 1989. Some chapter titles: "Where does beach sand come from," "What can I do about my eroding beach," "Shoreline engineering: stabilizing the unstable," "Selecting a site on the Maine coast," "Coastal land use and the law in Maine," "Coastal forces: design requirements," "Building or buying a house near the beach." You get the idea. An incredibly useful and practical book about erosion, coastal dynamics, and building near the ocean.
Lobster: A Global History, Elisabeth Townsend, 2011. This one might seem like it belongs in the marine biology section, but it is part of "The Edible Series," and while it does cover the different species of lobsters the primary focus is on who has been eating them over the centuries, and how they were prepared. On the whole an interesting little book, although far too much space is devoted to humane contemporary ways of killing lobsters. I would have been satisfied with a summary of that!
 


 
