Car chargers are a dime-a-dozen, but lets you charge your Nexus 7 on the go. Expensive device chargers can pump out enough juice to charge the tablet and at least won't ruin thes battery.
* Tmvel Gadi 10W 5V/2A Dual Port High Speed USB Car Charger - Heavy Duty
This accessory is compact and light weight. Simply Plug the Tmvel Gadi into your car cigarette port. The Easy-to-see LED displays if the device is connected.
* CrazyOnDigital Dual Car Charger DC Adapter with dual USB Cable, Black
It has two built-in different cables (mini and micro USB), and one plug for 1amp and another for 2amp capability devices. It works well, but doesn't fit well within the cigarette lighter socket.
* Arcadia Rapiduo, 10W 5V/2A Dual Port high-speed USB car charger w/ Free Full Speed Micro-USB Charging Cable (IMP80C)
It is small with sleek design. With dual USB ports, you can charge N7 tablet and a second device at the same time as well. Doing a nice job while using the tablet for GPS.