Suggestions for ID sources?

[wateryworld]

I've been given a monumental task this past week of sorting through boxes of shells, probably a couple thousand or so, that my friend who owns a shell/mineral business has never gotten around to sorting himself.  Today we were discussing how, even though he's been doing this for around 50 years, ID'ing is still the most problematic thing for him because of the sheer number of species.  As someone brand new to the hobby, I can only imagine how daunting this may be.

Since the internet doesn't seem to be very easily helpful, since for the most part you need a clue on what you have before you can do a search on it (like to know what kind of turban you have, you need to know it's a turban in the *first* place)  what sorts of books can you suggest? 

I can't imagine having to consider buying a separate book for each of the vast varieties of shells out there!  What books, sites, or other sources would be the most comprehensive, without having to buy a boatload of stuff?  Seashells of North America: A Guide to Field Identification by Tucker Abbott is one I'm currently looking at getting, circa 2001.  The one my friend uses is the 1968 version, but I don't like the idea of getting really outdated books since so much changes in the field so frequently. 

And like I mentioned in another thread, having so few people on this site, and having to wait a month or so to get a *possible* response, IF any response at all, is not helpful in the long run so I must supplement my learning tools a bit

Suggestions?

Thanks