I just performed my Random Act of Publicity for a favorite book (yet to be featured, so I'm not saying which) by writing a review on Amazon.com. Now that I've done it, I can't believe that I haven't before. Really, quite painless! And perhaps it will nudge a deserving book into the hands of new readers.
If you love to read (and I doubt you'd be reading this if you don't), I recommend taking a few moments out of your week to promote a good book. Spread the word! Maybe "your" book will go viral, in a good way. Or at least sell enough copies to stay in print for another year.