EastCoast intake systems
http://www.ecisbmw.com/DMCart/
cost me about $450 2-3 years ago, and on sold it to another Bimmersporter in Hamilton, can t remember his name though.
(I changed from E36 323 coupe to E46 325 Coupe)
I recon about 7 HP, but got rid of flat spot. Sounded great too. Thinking about one for E46.
A mate had one in his E46 330, recons it was great.