haha... way to be vauge? Hmm, my advice. if you're going to get the intake, you may as well get the headers for your car. Either get them custom made - or you could order them from Bav-auto (richman website...@_@), Ireland Engineering (good products!), or turnermotorsports.com. Also, a few guys distributing for IE just opened up a page at seambmw.com, they don't have the engine upgrades page up yet but I'm sure they're working on it. You may check them out as well.
Short of headers and your plan for intake, I'd say you could get a slightly more aggressive cam, make sure to replace the springs while you're at that (valvetrain.) and the valves as well. Other bolt ons you could get... well, I'd advise getting a 4 core aluminum radiator and then hooking up a twin electric fan setup. That'll free up some power from your engine. I've had a friend advise an electric water pump setup, but you'd have to change thermostats in the winter and shiz... Uhhh... lets see. You could... I guess get a dyno-tuned mapping to increase your fuel flow and all that to optimize horsepower. Thats not too bad. Not really a bolt on, but I'll bet your local speed shop could do it pretty easy. Anyhow, I'm out of ideas. haha. Bolt ons seem kind of limited in general... @_@