What size are your tires? Also, how light are you trying to get? If your tires are 2.0" knobbies or larger, your greatest gain will come from changing tires. Besides saving weight, narrow tires are going to make you faster by reducing rolling resistance.
Shaving grams can get very expensive. I personally wouldn't go beyond getting a lighter, narrower set of tires and if you're still not satisfied, I would buy a new bike. As others have already pointed out, 30 lbs is about average for a commuter. Changing tires should give you a sub 30 lb bike.
You're planning to spend between $850.00-$900.00 to shave grams on your bike. For that kind of money, you could buy a second bike under 25 lbs, and you could have two bikes.
You might also consider going to a single speed. These bikes with a set of narrow tires are lightweight due to a lack of shifters, shifter cables, a cassette, a second/third chainring, rear de-raileur, and front de-raileur. They are also much quieter. Instead of replacing parts on your old bike, buy a new bike that's stripped of all the above parts, and you'll save some weight.
Last edited by City_Smasher; 04-19-08 at 09:31 AM.