lol this thread is so off topic. i know its a rerun, but he didnt get much info last time either.
basic performance bolt ons are: hi-flow intake (air filter upgrade); hi-flow muffler and/or exhaust; header.
if you can do the head swap (as described in the reference section article), it would be cheaper. and you can add the bolt-ons later. it sounds like maybe the head swap might be a litle too much for u to consider right now, since u are asking about basic/easy mods.
guidelines for the basic bolt-ons:
its best to buy them in this order: 1) hi-flow intake 2) header 3) hi-flow muffler and/or larger exhaust piping (i would suggest no larger than 2" for your stock hf engine, to prevent too much backpressure loss).
here are some very good, reputable (and not cheap) brands to check out:
for intakes/air filters: AEM, K&N, injen
for headers: DC sports, chikara, greddy
for mufflers/exhaust systems: apex, tanabe, greddy