I've been running K&N, but I just ordered four of the Neutron Safe Guard filters from RMATV to try, they got excellent reviews, as good as K&N and OEM both, and the price was much, much better. $3.99 a filter. They are closeouts, so if anyone is interested, I'd jump on them while they still got them, lol.
'01 Raptor 660: 101mm 11:1 Wiseco, HCII, P&P, Curtis Sparks Exhaust, ProFlo w/ K&N, ACE Fabrication +2+1, JTM, G-Force Extended Axle, Holeshot HD, Holeshot XCR, Haulers, ProTaper SE Raptor Bend, ProTaper Pillow Top Grips, ASV Clutch Lever
'07 Raptor 700: 11.5:1 Tech, X4, Bo White +1 port, +3 TB, Curtis Sparks Exhaust (shortied), FCI w/o box, PC3, FullFlight +2+1, G-Force Extended Axle, Holeshot HD, Holeshot XCR, Haulers, Fasst Flexx, OURY Grips, ASV Shorties, Jogaca Suspension work