The Internet is a handy wee thing. In addition to one or two other things, it can be used to keep track of what you’ve read, what you’re reading, what you want to read, and what other people recommend that you read. I’ve been using Visual Bookshelf via Facebook over the past year and I’ve found it to be quite good, if a little clunky. It does recommend books I might like, but not as well as the popular LibraryThing. BookRabbit is similar, but I’m not sure which is better (it looks nicer, if that matters). There’s also Goodreads, Bibliophil, and Booksie (for sharing your own stories). There’s Listbook.net, and also Shelfari, which lets users create a bookshelf to show off their latest books.
You could also just use a notebook – no one else would know what you like – but it’s a noble excuse to buy a moleskine, I reckon.