(in the UK)
I purchased the sony prs-505 and am seriously impressed. So far I have gone from 1 book every 6 months to one per day (will probably tail off).
Also the battery is still on full

Main development points for sony is to get rid of the annoying black flick when pages change, and also to increase the screen size without increasing the device size.
Sony provided 100 free classics with the device. I bought a DVD pack of 11k out of copyright books from ebay for £8.99 and further discovered Gutenberg.org which is a library of out of copyright books (most are in epub format, which is an open source ebook format which the sony can read) with over 28k directly accessable and another 100k available from links with associates.
In terms of purchasing copyright books, whsmith and waterstones on line have all the latest bestsellers and equivalents for most of their paper books.
The sony can store around 160 books in memory, but has both an SDHC and a memory stick socket. Although on the forums it seems that over around 10k books is difficult to organise on the PRS-505 at once (due to the 200mhz cpu building the library).
The other interesting effect of this type of device is that you can keep many books on the go at the same time, swapping between them to read a chapter or so at ease. This is not practical with conventional books and puts forward a entirely new way to digest literature.
Currently I have on mine 35 books. To give an example of the type of books that are available free:
1. Zionism and anti-semitism: Max Nordau
2. With our army in Palestine: Antony Bluett
3. The wicked earl: Margaret McPhee
4. Uncle Vanya: Anton Checkov
5. A traveller in war-time: Winston Churchill (the US write, not the UK one!)
6. Thus spake zarathustra: Friedrich Nietzsche
7. Three contributions to the theory of sex: Sigmund freud
8. Poison study: Maria snyder
9. Pearl-maiden: H rider Haggard
10. On the significance of science and art: Leo Tolstoy
11. Moon of Israel: H Rider Haggard
12. Merely Mary Ann: Israel Zangwill
13. The melting-pot: Israel Zangwill
14. Love and other stories: Anton Checkov
15. Letters to his children: Theodore rooselevelt
16. The Jewish State: Theodore Herzl
17. The hunting of the snark: Lewis Carroll
18. The grey wig stories and novelettes: Israel Zangwill
19. English lord, ordinary lady: Fiona harper
20. The crisis complete: Winston Churchill
21. Chosen peoples: Israel Zangwill
22. The blue zone: Andrew Gross
23. The art of war: 6th cent B.C. sunzi
24. Alice’s adventures in wonderland: Lewis Carroll
Truely, a breakthrough device