I like Crutchfield. Yes there is always someplace cheaper but when I order from Crutchfield I get everything I need for the install included. The wiring harness for my car is included. The dash mount for my car is included. Printed instructions for my car are included. They have a lot of good resources including forums, videos and instructions.
http://www.crutchfield.com/app/car/mycar.aspx?
http://www.crutchfield.com/app/car/mycar.aspx?