I hooked up a receiver I got from amazon:
Amazon.com: Kenwood KDC-MP345U In-Dash CD/MP3/WMA/iPod Receiver with USB/Aux Input: Electronics
...using this wiring harness:
Amazon.com: Metra 70-2003 Radio Wiring Harness For GM 98-Up Harness: Electronics
The car is a 2004 cavalier, and I used...