Which is your can't-live-without cell accessory?

There are just so many accessories and add-ons for cell phones these days that they are no longer just a communication tool, they have morphed into our personal assistants, music and video stations, cameras, blogging tools, mapping assistants and much much more. I sometimes find it confusing to figure what exactly I need besides the phone itself. Like there are lots of RAZR accessories products on Wirefly's newly relaunched site and but I'm still not really sure if I would need some accessories. For the business professional who travels a lot, the hands free and bluetooth options are almost necessity. The one item that makes the most sense for me is the car charger, since I'm always running out of battery when I'm traveling.