I use the Hiflofiltro filter #123. I get them at my local Yamaha dealer here in town for about $4 each. Personally, I think Fram filters in any form are about the cheapest quality filters out there. The K&N 123 is also good, but not worth the extra cost in my opinion. Wix filters are of very good quality as are Napa filters. Wix and Napa can be had at your local auto parts stores. If not carried as normal stock they can be gotten usually by the next business day as the distributor they get their stock from has them in the warehouse.