The Mopar iPod kit works great if you have an REC (sat nav) or RAQ (6-disc) radio (shows artist/track, etc.) The only problem is that they have some issues with newer iPods (Classic and iTouch) and iPhones (due to Apple updating firmware). Even Peripheral brand has some issues. I had the Mopar kit but took it out because it quit working with my iPhone when I updated to 1.1.4. Now, with 2.0 it may work; I don't know.
From what I understand, a company called 'USA-Spec' makes some kits that work fine with all the new iPods/iPhones. But I couldn't tell you for sure...that's what a buddy of mine who has a Peripheral one told me (since his isn't working 100% with his 80gb Classic).
Of course, if you have the rear DVd system, you could just get an RCA adapter and use the inputs on it...
2006 Bright Silver Grand Cherokee Laredo
3.7L 4WD ("mostly" stock)