Thanks for the advice. After doing some more research I'm debating between the following:
1. Leave the stock radio in and adding a DIY auxiliary input (directions in the How-To section). The radio is in good condition except for some of the lights being burned out (one inside display and some buttons). Maybe using some of the money I save to buy better speakers.
2. Leave stock radio and buy an adapter plug (AAI-GM12). Seems like less fuss and more reliable.
3. Buy a cheaper radio (around $100) and the harness.
I'd be interested on everyone's opinions on which is best. It's a family car and we're not into loud music or a lot of base.