Hey there and welcome back to Teh Werkz! There are oh so many options to choose from - all depending upon your needs and wallet size! Getting your ECU chip reprogrammed to boost engine power, rev limited and elimanate speed restrictions is one thing. Supercharging (or, of course even a turbo) - use of forced induction is the biggest way to increase your power. Many choices are totally reversable too! But first things first - if you are buying your new bestial prize new or just about new, you have the full coverage package from BMWUSA/the dealer for service and even most wear and tear for the first many thousand miles and several years. If you make changes on your own like touched on above, you will almost definitely VOID this coverage
- this is something I would advise verty careful though on. The only way around this I know of is to get these mods done BY THE DEALER when you buy the car. BMW used to use Dinan, a top industry brand in doing these types of pre-sale mods, and they do not void the warranties, but you will surely pay a fat premium. I think this year BMW's contract with Dinan is over and they are using their own forced induction products. You can and should check all this with your dealer.
All the above said, top tuners are all over. KO Performance in FL, a web based company with a great rep has several good and cost-reasonable choices for beefing up the power. Same with BavAuto as Wonderboy told you above. Top brands are Dinan, VF Engineering, Active Autowerkz, UUC and others.
Where do you live?? If you choose to puruse more power as above, first off you need a top race shop to get it done right and keep it running right!
Last thing is that even though you have a new ///M car, once you start beefing up power, you need to start thinking about better brakes (eg Brembos) as with great power comes great stopping responsibility! Lightweight clutch and flywheel, better exhaust, etc etc all boost hp. This can get expensive and fast my friend (I know whereof I speak!)
I hope this stuff helps. Enjoy your new ride and remember - there is pretty much NEVER enough power!