A couple of my favorite ebookstores:
Baen Books (via
Webscription)
BookView Cafe
(
O'Reilly is another one, but you don't strike me as the type who's looking for a good programming reference)
Personally, I'm more of a classics reader -- I actually bought my PRS-505 so I could read
Project Gutenberg in bed!
If you just want to read whatever other people are reading, you're going to have a harder time of it; aside from the DRM, you're also going to pay more for an ebook than a physical book, in many cases. Check your local library for alternatives.
If everyone refuses to buy DRM-restricted books, though, and tells the publishers so (and ignores their spin about how our books have to be "protected" from us, because we're evil and all that), they'll get a clue. Money talks. Selling DRM-free books is working very well for O'Reilly, Baen, etc., who are major publishers in their specialties. If it works for them, it can work for the generalized publishers ... so long as we refuse to pay more for books we can use less.