There are plenty of on-line stores selling DRM free ebooks out there. Even though it is going down hill as far as selection and quality is concerned,
www.fictionwise.com still has an ok selection of books.
www.manybooks.net is a good source for free ebooks (all of which are, of course, DRM free as well).
www.feedbooks.com has a good selection of indie books.
There are plenty more out there, but this should give you a good starting point.