You can buy/obtain some legal DRM-free ebooks from:
- This forum (public domain books)
- Manybooks.net (public domain books)
- Fictionwise (choose only 'multiformat' books)
- Smashwords (indie/self-published books)
- Baen Books (sci-fi publisher)
If you are interested in indie books, I have been compiling an
Indie eBook Hall of Fame where books can only be listed there if three independent bloggers have positively reviewed them. It's meant to be a good starting point for people like you

You might also be interested in the
Backlist Ebooks group, these are authors who were commercially published and later regained the rights to their backlist titles, which they are now re-publishing.