What can I do to make my jeep sound/run better?

I have a jeep cherokee with a little 4 cyl engine. I love the car and would like to make some inprovements to the engine since its pretty stock right now. What are some things I could improve to make it sound better or meaner? I was thinking a new muffler and air intake, any recommendations/suggestions? I'm also on a budget too so nothing crazy expensive.