For the guys with pre 92 stangs (with the 4 lug) the 10 hole stock ford rims are very light and are quite good for the front. You cant really fit slicks on them though.
We have a set of F1 wheels off the Micheal Schumacher Ferrari from last year. They were used in a practice event and re-finished by BBS. The fron one weighs.....5.9lbs!! It's insane. If you are in the store check them out on the wheel wall and pick one up. Just don't drop it!
OMG ill make sure to steal one next time i go. i had VIP passes 3 years ago for the pits and touched one tire. i was in pain for 20 minutes cuz those tires are boiling hot when they come off the cars.
Volk Racing TE-37 MAG is the lightest wheels for it's size I think the 17's weigh like 8lbs...they are money though and you need to do a single lug conversion.
They had an issue of sport compact magazine which showed a sh*tload of wheels and their weights, and I noticed a company named Velox had one of the lightest street ones...their 17 inch rev-10 weighs 11.5lbs.
SSR make some decent ones, I think mine are about 16.5LBS in 17x7.5, BBS too but carefull with them...not all are forged and not all are particularly light weight.