The $149 LevelOne MobileSpot is really a pretty simple idea. Take a fairly standard portable 802.11b/g wireless router and build in a PC Card slot and USB port that lets you turn a 3G wireless PC Card or USB modem into an instant hotspot. Then basically all you need is a decent signal and you can set up a network just about anywhere.
The MobileSpot (WBR-3800) can also be used with a cable or DSL modem connected by Ethernet allowing you to leave the 3G option as backup, so there's less chance your connection will ever be interrupted. It's reasonably compact, too, at 5.1 inches wide by 4.8 inches deep by 1.3 inches high and weighs in at 11.2 ounces.
Security includes a double firewall, WEP, WPA-PSK, WPA2-PSK, and TKIP/AES Wireless encryption support, and support for VPN pass-through of PPTP, L2TP, and IPSec secured data connections.