I have a Densecharger CAI and thought it was a decent upgrade over the factory air filter setup. I can't tell exactly how much I gained with it (no baseline performed before/after the densecharger), but when you're trying to squeeze out every last bit of horsepower from your motor, it won't hurt you...be warned though, you won't gain as much on a NA motor when compared to blown motor. There's plenty of other choices too: WMS, BBK, MAC, or you can make your own (Home Depot parts)...
The important thing to remember is to draw your air from a cool source when installing a CAI system (the "sticking an exposed air filter element under the hood" theory can work AGAINST you, especially during the summertime. The underhood air temps will make the inlet air temp skyrocket. Run a search for user "postban" - he did a comparo complete with temperature measurements on this topic, maybe a year or so ago).