Seconded, they are extremely versatile, but make sure you do some research on how to use them effectively (books, videos, or trainers). Their unconventional shape, which makes them so effective, also makes it easy to lift in a way that is bio-mechanically unsound. Also, there are a huge number of compound lifts that you would never think of on your own (e.g., the Turkish Get Up—not a beginners' move for sure: http://www.youtube.com/watch?v=uGRBvom4Zrw)