I really like the Hamann HM2's. Especially if you are set on 18's.
One thing to consider is if you have/will have suspension work done. I just reciently did suspension work and had 17x8.5 SSR GT2's w/ 235 rubber and I have some minor issues w/ rubbing (http://www.unitedbimmer.com/forums/thread2228.html
) . If you want big 18's you might have to modify the wheel well.