The most popular mod would be a new exhaust system. The Eisenmann Race Exhaust might be right for a performance minded individual like yourself. They also offer a toned down Sport version.

I put 30mm spacers on my rear wheels. I love the look. The stock width is just too narrow for my lies. Check under my posts or serch for before and after pics of my X with the spacers.

You may want to purchase the BMW running boards. They have a great look to them. They really finish off the look of the sides of the X.

Superchip offers a chip for the 4.8. The power increase does not seem worth the $1,500:

http://www.powerchipgroup.com/intera...sp?pid=Bmw0182

The increase for the 4.6is is much greater. Supposedly 27hp....

As far as Cold Air Intakes go read my post regarding them and let me know if you have any questions about the various ones offered. I do not love anything currently out there.

Lowering is also quite a popular mod. Personally I like my X with a bit of height but there are some great looking X5's on this site that have been lowered.

Tell you what you need.... a Brembo Big Brake Kit! Quite costly at $4,500 but damn it looks great!! They are somewhere on my X5 "someday" wishlist!!

Good luck with the X!! When are you going to get either the GT3 RS or the 07 Twin Turbo??? Two quite badass cars! They are also on my wishlist!!