My goal is simple: to be able to listen to iPod in car with minimum effort. Thus, I choose cassette adapter instead of wired FM modulator. To my surprise, the sound is actually decent. Although there is some hiss when the music is off, I can't hear any hiss when I am actually on the road with music on.

My total spending:

XtremeMac cassette adapter: $17.95
Napolex Suspended Pocket: $8.99

I also use iPod with Arkon Vent Mount when I am not using the GPS. I receive the Arkon Vent Mount for free when I purchase my GPS from www.semsons.com (http://www.semsons.com) The iPod fits very well in the Arkon Vent Mount and feels very secure.