What performance mods, reasonably priced (meaning no superchargers, lol) are worth the money?

My truck already has a cold air intake and an exhaust system (Flowmaster 40 series), but would little things like putting on an aftermarket fuel/oil filter be worth the money?

What other little modifications could I make that would add to the performance of my truck without putting a hole in my wallet?

If you say headers, I'll shoot you I just had a horrible experience with some defective Hedman Hedders...wasted a lot of time and money...won't be trying headers again for a while.

Thanks in advance for your advice.

--Matt