Bought a Kindle a month or so ago and this is the best deal I have seen for some decent books at up to 75% off.
Begrudge buying them normally if they cost more than paperback version. Most books under £1.50. I chose several which had good reviews.
Normally the only cheap books for the kindle are those written specifically for the Kindle.
Even if you don't have a kindle you can download the kindle software for free on your pc/netbook etc and read it on there.