Honestly: Do something different. Do something that shows you know me. Don't follow a gift giving guide, don't follow the advice your girlfriends gave you over dinner.
Sex is sex. Yes, it's wonderful.. and I realize I may be the ONLY man to ever say this.. but I'd rather have something heartfelt and unique. I, as a man am tired of people thinking along the lines of "Oh, just give him a blow job and piece of ass.. He'll love it"
I realize this isn't the most helpful answer as every man is different, but find out what the man you are buying for really enjoys. For me.. I'm a photographer. If a woman handed me a box full of prints of my pictures or one of my pieces custom printed in a nice frame.. I would never forget that.