Have you discovered Goodreads yet?
I've been using it to keep track of the books I read for several years now. It's a wonderful way for me to remember that book I read, the one about the boy, oh what was it's name again? My reviews aren't masterpiece reading, as they're meant more to trigger my own memory in later years. Often I'll include some of my favorite quotes so that I can quickly find them again when necessary. You can sort the books you've read by date you've read them, by how you rate them, and in other ways and you can add books to various lists if you want, such as "books that would be good for teenagers" or "favorite parenting books." I have a list of my top favorite children's books, for instance. There's also a "books I'm currently reading" page, but I use that mostly for books I've checked out of the library and have had to return before finishing so I'll remember to pick them up again.
You can connect to friends, like in other social networking sites, and then you can get updates on what they're reading and how they rate their books. My two favorite features of the site is one, being able to see what my friends are reading and how they rate those books, and two, the to-read bookshelf. I love being able to keep track of books I'd like to read sometime and then putting them on hold at my library on occasion.
Here's a few of the best books I've read and rated 5 stars since joining the site:
The Screwtape Letters
The Boy Who Was Raised As a Dog: And Other Stories from a Child Psychiatrist's Notebook: What Traumatized Children Can Teach Us About Loss, Love and Healing
The Prize Winner of Defiance Ohio
Moving in His Majesty and Power
Broken Things to Mend
You can see my entire "read" list here, sorted with the highest rated first.