Aftermarket parts are a good start. Headers and smaller mufflers dump an amazing amount of weight. Like joshacu said, the window washer is another good 5 lbs if it's full. Sound insulation can be removed from under the carpet. If your car is like my Neon, there are a few useless braces and weights bolted here and there for decreased noise and vibration that can go. Lighter rims are also a plus.