Create a playlist on Youtube and watch it on your iPhone.
You no longer need to sync your iPod/iPhone songs with your iTunes library. You can create a playlist on Youtube.com by adding your favorite Youtube videos to the list in the convenience of your desktop and play back the songs on your device using this application.
With this application you can search for and play any playlist that is publicly available on Youtube.
Optionally, if you connect an FM transmitter to your iPhone you will be able to stream songs from Youtube directly to your car stereo.