You have a lot of options. Check out some of these threads they should help you decide what upgrades/change you want to make. And welcome to the forums!

http://www.xoutpost.com/articles/x5/...ctory-amp.html

http://www.xoutpost.com/articles/x5/...6is-janix.html

http://www.xoutpost.com/articles/x5/...id-bmw-x5.html