I helped a buddy of mine put one of these in his Hyundai a few years back.
http://www.amazon.com/iSimple-IS31-A.../dp/B002U5XPBE
He's been pretty happy with it so far.
Sonic Electronix or Crutchfield would have more customized kits that wouldn't use the antenna and might give you a little better audio quality but those would be a little more expensive.