Do you have any major travel plans for the near future? If so, the ZTE AD3700 from Verizon might be your best bet. This USB-plug in modem has pretty much every sort of connection you'll encounter anywhere you travel. EV-DO, UMTS, GSM, GPRS and EDGE are all covered. This modem connects via USB and can swivel to fit any sort of computing arrangement you might have.
The AD3700 will be in stores tomorrow. It starts at $79.99 for a 2-year mobile broadband contract after a $50 mail in rebate. This modem is compatible with Windows Vista, XP, and 2000. You can check out its page here for more information.