I didn't see this mentioned. FreedomPop offers free wireless internet access based on the Sprint network. (For what it is.) You just buy a MiFi hotspot that runs off a USB outlet (so you can run it off your cigarette lighter) and you get 500MB a month. That's very little, especially since your computer updates in the background and such. But if you use it sporadically it's great. You can buy more data but that gets pricey.
If you use it, be sure to disable the automatic top-off or it'll charge when you run over.
They also have an unlimited phone service, which includes tethering to your laptop, for $20/month. Unlimited text, voice, and data. Not bad. This is clearly a better choice if your internet usage is more than just sporadic.