My vote goes to the Cantrell Concepts / Science of Speed intake duct that replaces the baffle with a duct that routes the entire left-side vent up into the airbox. The sound is awesome, especially with the driver's window open. I won't vouch for performance, but lots of people have sworn it makes a difference (although you won't see it on a dyno). I did see an accelleration difference of maybe .01g on a g-tech pro in second gear from 30 to 80mph, but that's small enough that it's more likely due to a subtle difference in positioning of the unit, or a change in ambient temperature, or something.
One note about it, though, is that I would NOT use a K&N drop-in filter with that intake. The reason being that I live in Seattle, and through winter the roads are wet about 5 days out of 7, and I can only imagine how much mist is going through my intake. The stock filter has been dealing with it just fine (front is dirty, back is clean), but I'd really worry about that much moisture going through a K&N. I have a feeling it'd tend to wash the oil out of it, leaving it in a condition where it wouldn't filter well at all. That, however, is all speculation. I haven't even actually inspected my stock filter after driving through mist to see how wet it is (or if it's even wet at all).
-Mike