Personally I would go with a JL Cleansweep if you can swing it, but they are on the expensive side if you are just wanting decent sound and not totally anal about your sound quality
Lots of people suggest the Navone LOC, I think it might be a little pricey too, not sure about athat one. But really,Just about any LOC would work. For the short time I had my stock radio I just picked up a 15 dollar one from RadioShack, Im not even sure what kind it was. Metra maybe. Worked perfectly fine. That was a couple years ago, and the same LOC is hooked up in my buddy's Grand Prix with no problems from it.