DAZ Software releases Wi-Fi Login Pro, an inexpensive WPA/WPA2 Enterprise server: The enterprise flavor of WPA/WPA2 requires each user who wants to gain access to the network to have a user name and password. (Some systems support other credentials, like smart cards or certificates.) Wi-Fi Login Pro joins Periodik Labs's lower-end Elektron server (Mac OS X, Windows; $300; unlimited users). Wi-Fi Login Pro runs $200 for 100 users, but is designed for somewhat simpler administration. There's a trial version.
I recommend that any business of more than a few employees consider WPA/WPA2 Enterprise. Each logged in user's system is assigned a unique encryption key, and credentials can be revoked if someone leaves the firm. WPA/WPA2 Enterprise isn't foolproof, but a cracker can't bruteforce his or her way through; and social engineering might allow one user name and password to be obtained, but, unlike the WPA/WPA2 Personal system, that doesn't compromise other user's sessions because they have unique encryption keys.