I run the Dinan CAI and I love it. The sound is deep and throuty... but not too loud. If you're running at low rpms with normal driving (everyday commuting) it sounds stock, completely silent... but the SECOND you hit that pedal hard, the thing roars.
That allows you to drive in front of starbucks with a bunch of people outside without drawing too much attention if you don't want it... or punch it for all the attention from everyone around.
If you get a CAI though, a chip or shark injector is also a good idea... the two work well together.