if u could post some pics of your car (so we can see what we're working with, as opposed to just looking for generic '03 325 pics on google), that'd probably help solicit some more responses.
also, providing information like intended use, budget, lighting laws, etc. would help
like Rl1 said, the UK cops use BMWs a lot so it wouldn't hurt to look in that direction. however, from my experience, most of their installs on sedans are pretty limited to a beacon on the roof and maybe some grill lights, so u may not get too far there