Before all you overly eager, mod happy freaks go out and blow a bunch of coin on something your car doesnt really need, but absolutely must have
take a gander at this ----> http://www.mkiv.com/techarticles/filters_test/2/
Injen and AEM both make their own filter elements and are comparable to K&N's. APS uses a K&N filter element with their kits as do a lot of other manufacturers, if not you can usually buy a K&N element to fit most of the aftermarket ones. Wet foam type filters also have 1 major drawback, over time your MAF sensor may get fouled by the oil and throw a CEL, or worse, eventually damage it and cost you even more $ for repair/replacement (trust me on this) lol, plus, they're no fun to clean and re-oil. If you don't care about looks under the hood or a cool BOV sound keep your stock air intake, save your money and just upgrade your panel filter. Hope this helps, cheers!
P.S. If you live anyplace overly wet you'll regret blowing all that $ on a CAI, fair warning.