Getting more power can be as simple as a tune up or could be changing parts. Obviously you want to make sure the tune is good. Then if you want more power you will have to dive into the engine. If you dont have headers and dual exhaust that is one of the first things you should do. A performer intake would show some better performance over a stock intake but probably not a real noticable difference.
If you are pulling the heads for head gaskets you could swap to a better head. Vortecs are cheap and make more power than any other oem head. This does require a new intake, valve covers and rocker arms but you will see a increase in compression, still low enough for our junk CA gas, and a increase in power.
You can also add a camshaft but dont go too crazy. I have actually been considering this camshaft,
http://www.summitracing.com/parts/lun-90350lk/overview/
Should be a direct "bolt in" meaning stock rockers, pushrods and springs. Would work well with either your stock heads or the vortecs.