I love Pixel of Ink, one of the sites Julie linked to. If you read YA books, they also have a YA/Kids site. Sometimes the books on it are the same as on the main site, sometimes not.
Most (all?) library Kindle lending happens through Overdrive. You can find out through there if your library participates. But some of the biggest publishers don't allow library e-book lending, so even libraries with an extensive Kindle collection may not have some of the most popular books that you'd expect them to have.
Although these aren't free, the Kindle store has a Daily Deal (usually $.99-$2.99) and 100 books each month that are on sale for $3.99 or less. You can find them by going to the Kindle store (from your computer, not your Kindle) and clicking on Kindle Books, then there's a listing for each of them. Pixel of Ink always covers the Daily Deal and includes at least some of the monthly books mixed in with its other listings.
DH listens to some Kindle podcasts where he learns all sorts of tricks. I know he found a site that you can put books on a watch list for when they have price changes.
These are great suggestions! Do any of these sites actually review or screen books? I've found that so many free books are pretty bad and not necessarily worth reading, even if they are free.
These are great suggestions! Do any of these sites actually review or screen books? I've found that so many free books are pretty bad and not necessarily worth reading, even if they are free.