383 stroker. Good all around motor, reliable, plenty of torque and horsepower. Best of all they're readily available as crate motors from quite a few outfits and not all the pricey either.
Depends on your budget. If under 7500 then go with a LS1. Very reliable, Very light (Aluminum) Good stock power (310 or better) and easily modable for very little money. You can make 500 hp for under 1500 dollars worth of aftermarket stuff.