I mentioned in my last review that my phone gives me a free book every month, and someone asked me privately how that happens. I figure others may not know about this either (took me ages to notice it) and it's a nice offer.
If you have a Kindle account and a Samsung device of pretty much any kind, and you make a Samsung account (a really good idea anyway, because their "Find my mobile" service is faaantastic and free), you can go to the Galaxy Apps store and download the "Kindle for Samsung" app.
Kindle for Samsung is in every other way exactly like the normal Kindle app, except once a month it lets you pick one book out of a selection of four free books offered by Amazon. There's generally a fantasy or sci-fi, a "literary" and a thriller type, and the fourth is often chick lit or women's fiction although it does vary. Most months I look, there's at least one that I'm more or less likely to read.
These aren't loans, the books are completely free, lending enabled, Whispersync if it's available, etc. So even if you don't read on your phone, it might be worth grabbing the app there just to check out the books.
There's a thread here at Mobileread where you can look back at the kind of books that have been offered, but of the few I've remembered to actually get and read (blame my memory, not the selection) I've been pretty impressed.
(post #176 has this month's ones, for instance)