Crutchfield. Here's the one I bought:
http://www.crutchfield.com/p_120ASWC...C.html?tp=3405
They have two of them there, but not only did I see better reviews for this one, but when I brought to the shop who did the install, the guy thanked me for buying the good one.
Little pricey for what it is, but it works perfectly.