I got a Monster Cable iPod FM transmitter for my wife last Xmas. It'* just a cable (that doubles as the antenna), with a 12v plug (it charges, also) and a little inline module for switching FM stations. If you must go this route, I recommend this one because there are no hard plastic parts to break like in those models with arms and brackets and such.
However, I'm upgrading her to an iPAC OEM this Xmas, because the novelty of the FM transmitter wears off after about 5 minutes once you realize how crappy the sound transmission is, and the utility ends once you take a road trip and have to change the station every 3 minutes because of interference.
2004 Buick Lesabre Limited, Gran Touring; Bone Stock
1998 Buick Lesabre Limited, Gran Touring; Mods: Poly sway bushings/endlinks, Tru-Cool trans cooler, Thrasher shift kit (med), PLIM, front PEM; Mods in progress: Alot of stuff, but slowly...