I haven't been impressed with most of the current iPod adapters that are out there. I don't like the fact that with most of these you can't see the track names on the head unit, and that you can't control the unit from the head unit.
Harman Kardon is coming out with a standalone auto iPod adapter. You plug your ipod into this unit, and the display will show your iPod's controls. To control the iPod you will use this unit's control, so you can put your iPod in your glove box.
This looks like the best solution for people who don't have a head unit that can control an iPod directly, like the Alpine units.