The ones that stand out the most on my bookshelf are the Legends and Lairs series of books by FFG. I've enjoyed the hell out of those mostly because they're well written (IMO) and chock full of OGC (which is super important to me because it shows that they care about the importance of the open gaming movement). Another important set of books is Bastion Press' supplements (like Arms and Armor). The entire book (minus the trade dress and art) is OGC. The content is suitably impressive. I was hooked from the day I brought that gem home. :)
What does everyone else have on their shelves? How important is the OGL to you? Do you look to see how much of a product is OGC before you buy it? I'm genuinely curious about the whole thing.