What's a good, extensive DRM-free ebook library?

I run ubuntu linux, so my choices on book-buying are terribly limited and uncomfortable, with all the DRM encoding I have to remove for books I legally own. There has to be another way. I’ve been to many DRM-free sites, but they just have public/project gutenberg titles or books I don’t want. Is there a site that has a library comparable to Sony’s store (I have a PRS-300 but sony’s reader program doesn’t work on linux) or Amazon’s collection on Kindle?