The easiest way to add little hp to your Jeep is to address the intake and exhaust. Check out the link to the blog post below in the references section.

Airaid has an easy bolt-on cold-air intake kit that adds about 14 hp and can be purchased for about $225.

Borla, Magnaflow, Gibson and some others have cat-back exhaust kits that you can find for around $500 and should add another 10-12 hp.

Another item you can get is a hand-held computer tuner from Hypertech. The tuner will add about 8 hp on regular gas and 11 hp on premium gas. You should be able to find a Hypertech tuner for around $380.

What's great is that all of these products should also give you slightly better gas milage by making your motor motor efficient.

Good luck!