These days, there's a better than decent chance that your car can play MP3s on its own just fine, thank you very much. But for those of us not blessed with Sync or similar, the Griffin iTrip does the trick.
The new iTrip Universal is the same basic story as previous models: plug it into virtually any music player (iPad, Zune, CD player, etc.), listen to it through any nearby FM receiver. It's a road trip boon, and for $25 (plus an optional $20 car mount), not a bad stocking stuffer. [Griffin via iLounge]