Smashwords.com is basically the Lulu of ebooks--self-published ebooks in a variety of formats, often with a percentage offered as a free sample, has both individual author selections & small publishers. No DRM, good prices.
BooksForABuck.com: "Your source for affordable electronic fiction." Not all $1 or under, but a solid selection are, and most offered in several DRM-free formats.
A lot of small genre publishers have Sony compatible ebooks, either DRM'd ADE books, or non-DRM'd ebooks (unfortunately, sometimes only PDFs).
Samhain Publishing: Romance, erotica, supernatural books
Freya's Bower: Erotica & romance
(There's a cluster of erotica/romance/supernatural/fantasy ebook stores; I'm not going to try to list them all. Suffice to say, if you like one, there are several others competing for your eyeballs.)
FishesEye: "Ebook Store with an eye for the unusual! Ebook fiction and non-fiction for sale: humor, science fiction, internet & computing, how-to guides, poetry, crime, vintage travel, fashion and entertainment, cookery & recipe books." PDFs, and LIT version for most titles.
Double Dragon: Science fiction/Fantasy; large cluster of formats available, no DRM.
Spiritual Ebooks: Christian ebooks. PDFs.