If you got a Kindle device this year for the holidays, don't forget about the Kindle Store Daily Deals. There are always plenty of books for just $1.99, and they change daily. It's a great way to build your library on the cheap.
You need a Kindle or Kindle Fire to buy them, but once purchased they are in your Amazon account and can be read on any device with a Kindle app. With WhisperSync taking care of your bookmarks, you'll be hard pressed to find a better reading solution anywhere. To find them, just open the Kindle store from your tablet and look for the Daily Deals link on the right.
You'll always find deals and specials in the music and video store as well, but the Kindle deals are a solid perk for having one of Amazon's tablets. Take advantage of it if you like to read and have a Kindle device. I just picked up William Alexander's "The $64 Tomato" and plan on spending the evening enjoying the warm indoors with it.