Some big boasts from Monster at CES 2008, who are calling their iCarPlay 250 the "world's most advanced" iPod FM transmitter. Featuring a low-profile control unit with blue LCD display, three channel preset buttons and autoscan, the iCarPlay 250 trawls the FM spectrum not once but three times before selecting the clearest frequency; it can also adjust the power output on individual frequencies which will apparently ensure maximum clarity and strength.
The 12V cigarette lighter plug is attached to the dashboard unit via a removable USB plug, meaning you can use it to recharge any other device which gets its juice from a USB connection. Alternatively, the iCarPlay 250 can be powered from a laptop or desktop USB port, should you want to use it in your office instead.
I'd have to hear it in action to know whether the sound quality gets anywhere near a direct cable hookup to the car stereo, but a suggested price-tag of $99.95 seems reasonable.