I've used K&N panel filter and induction kits in my last Jeep (2007 Nissan Pathfinder-K&N Apollo kit) and currently have a K&N open cone induction kit in my 325ci.

http://www.knfilters.co.uk/search/product.aspx?Prod=57-1002

I know there are several people who will moan and grown (I've had the debate 1,000,000 times!) about them being an oil based filter and that they don't get enough cold air. I've used them for years and have never had a problem.

If you are going to go for one make sure you get one with its own cold air feed or one (like mine) which incorporates the OEM air scoop.

Completely agree with narusa ... it's all personal preference!

Did you get yours sorted?