Let the hive mind of Engadget get that for you.
"As someone who doesn't reside in the USA, I was wondering what would be the best way to get internet for my computer in the US for a couple of weeks? If it were Europe I know I'd look for some prepaid data. Is there anything similar offered by American carriers? A MiFi or a data SIM that I can tether from would work, but I'm trying to maintain a tight budget. Help!"
Yeah, we've carried these over at Sewell Direct for a few months. It's also nice because it does notify of WEP/WPA encryption and so forth. Not sure if this one does that. StarTech is such a funny beast. We were thinking of working with them before, but everything they make looks like they did it with an early-90's tech design in mind. Anyway, direct product link below:
http://sewelldirect.com/FreeCon-80211g-USB-dongle-WiFi-Detector.asp