Most ponies for the buck

[Skankin]

Don't waste money on an aftercat before you get rid of the stock 4 cat H-pipe. That's a common mistake. Even a high-flow H-pipe is WAY better. The stock headers should be fine right now... any larger, and you'd loose some low end.

Get a K/N filter.

An underdrive crank pulley is a GREAT idea. I recommend keeping the other pulleys though.

Some 1.7 cobra roller rockers will help it breath a little, and it's not nearly as labour intensive as a cam. Plus, the cam should really be the last thing you change... once you do the heads etc... it'll make everything work together.

Don't waste money on a throttle body either... you need an intake and heads before you'd see any benefit. An MAF might give you a little more though.