How does one get to review books ?

How does one get to review books ?

I realized yesterday when looking at my reading statistics for 2011 that I have done a great variety of reading. So, I was thinking if there was a way I can actually get books for review. I am not looking for any payments, just the books. And, a review (on Goodreads and on the blog) is assured.

Question is - where does one begin ?