Here's what I use on my Injen SRI:
K&N part# RC-3870
It fits perfectly. I replaced the Injen filter with the K&N and then cleaned the Injen filter with the K&N cleaning kit. When the K&N is dirty, I'll swap the cleaned Injen back on and clean the K&N. They are almost identical in size.
Amsoil just came out with filters to replace the coldair, short ram etc. Where the other filters end at the top, Amsoil cut it off and went back inside with more filter element, it looks like they have alot more filter area! You can check it out on their website and/or get one from a dealer.