Veteran wireless writer Eric Geier's AuthenticateMyWiFi has added a free option for WPA/WPA2 Enterprise authentication: I'm a long-time advocate of using 802.1X in the form of WPA/WPA2 Enterprise to secure every size of business's Wi-Fi network. 802.1X allows an administrator to set passwords for users, just as with a network share or other network login, while the Wi-Fi side of the equation creates unique master key material. No two users share this material, making snooping impossible; with a shared WPA/WPA2 Personal key, any user with the key can intercept all other traffic.
Geier's service is designed for all sizes of business that want to outsource the authentication system, but he's added a single access point option at no cost. Small businesses should leap (that's 802.1X humor) to try it out.
There used to be several companies and products that make it easy to outsource or install 802.1X. No more. Geier's appears to be the last that's focused on outsourced 802.1X management. You can use an 802.1X server on your network if you have Mac OS X Server 10.5 or 10.6; it's also part of some versions of Windows Server.