I for one got the Procede Enthusiast (
http://www.procedetuning.com/) for my N55 E90... once I get the car I'll let you know how it works, but all my research pointed me in the Procede direction and the new Enthusiast version isn't a stretch above the JB price-wise.
From what I've read this is definitely the best bang-for-buck mod that won't risk the BMW warranty (if you're careful).