Injen R/D cold air intake or AEM cold air with bypass valve. It will add a solid 9+ whp.
If you know a little about tuning, add the Apex'i SAFC II. You can gain more power by leaning out the fuel mixture.
Or you could opt for a cat back exhaust system. That will free up the exhaust flow and 3-4 whp.
Or if your car is fast enough for you right now, you could get the Road//Race Engineering Strut tower bar.
http://www.roadraceengineering.com/3g.htm for alot of proven products.
I put one on my car and the suspension felt so much tighter and flatter. $60-70 bucks.
If you are really into easy suspension work you can also get the Suspension Techniques sway bar. This alows you to corner better. This is around $125 bucks.