I found the most awesome site today -- WorldCat.org -- and I've now added book specific links to it.
What is it? It's a library catalog site -- lots of catalogs in one place. They've taken all the libraries in the country and put their catalogs in one place. This may not be important to you if you don't live in a major metropolitan area, but I live in L.A. If I want a book from the library system, I have to check 6 or 7 different web sites. Now I can go to 1 place and see which library in my area has the book. For instance I just found Georgette Heyer's old contemporaries that have never been reissued. It took me 10 seconds!!
Of course, I had to add this amazing site to FictionDB. Click on the anywhere on the site and you will be taken to the Buy page. We've now added direct links to WorldCat from this page.