Most of my friends are voracious readers, so anything that they mention reading and liking goes on an invisible list in my brain. If I hear good things about a book more than once, it gets bumped up the list. There are also a bunch of specific book blogs I follow. I like the Book Smugglers a lot, they're my favorite book bloggers right now. I also like Tia Nevitt's book blog, because she specifically highlights debuts, which are usually books I wouldn't hear of anywhere else.