I use a Remy 21798 alternator. It is 105 amp and weighs about 12 lbs. It is commonly available at just about any parts store. I run on Drag Week which involves street driving, plus there is no way for me to plug in a charger at the track. So I need a powerful alternator that I can buy anywhere in case it fails on the road, even tho it is heavy.
Edit: THis alternator is for a 1999 - 2004 silverado 1500. It is about the most power you can run off a single V belt, and it needs to be TIGHT. It comes with a serpentine pulley, and I had to put a V pulley on it. So if it dies on the road, I will have to swap the V pully onto the replacement alternator.