Not to much you can do that gives you much for your money
Some guys put 4.0 throttle bodies on. You can get them at a junk yard or off ebay pretty cheap.
Throttle body spacer... probably worthless
Intake... I guess
Headers are pretty expensive for the 2.5
gut the cat
I don't think anybody makes a chip for the 2.5 YJ
Personally I have done absolutely nothing to my 2.5