I really like my AFE Proguard 7 OEM style filter. Kind of expensive though (~80 bucks). It is better than the K&N in that it is 7 media layers of filtration rather than 2 and many others including AFE's standard filter which is 5. I also like the AMSOIL dry filter and am purchasing one to swap out in between cleanings when I clean my AFE PG7 as it is an oiled filter type.

 

Go all out!! get the amsoil 4510 big dog and ditch that air box!! A schedule 40 3" to 4" pvc adapter and your in buisness!! Sounds awesome and whistles like crazy!! What i like is it whistles like a semi when you are coming up to a stop and has that low whistle that sounds just mean!!!
ez