kindle has some free stuff....but from what i've read, they are hard to find and very limited. it appears that unless you have a kindle (or someone else with an account that you can use and transfer there books from), then some of the other ereader apps may be better.....for now.
I downloaded the kindle app on my motorola droid and was pleasantly suprised. I found a few reputable free books within the first few pages of listing in the amazon store: Alice in Wonderland, Sherlock holmes, and some others. I downloaded Alice in Wonderland, it has settings to adjust backlighting and background color, default settings will give you a migraine quick! Overall I think it is a good app, and you dont need a kindle to use it! Give it a try what can you lose it's free.