I like the stuff at the dealer. Klasse All in One for a polish followed by Klasse Sealant (maybe even a couple coats). Then you can put the was on top to add some depth.
This may have been posted here already, but it's the bible on many forums for newbs.
http://forums.bimmerforums.com/forum...d.php?t=158378
It's LONG, but totally worth the read.