I've been wanting to play with RADIUS, but motivation today quickly led to the discovery that is not going to happen short of dragging an old P2 out of the basement, finding a NIC somewhere, and hoping for the best with FreeRADIUS.
The manufacturers should market small, dedicated, RADIUS server hardware. Something like D-Link's DWL-2210AP, but dedicated to RADIUS only, without the rest of the BS in the DWL-2210AP such as the radios. Probably could even be small enough that it could just be a "module" that you simply stick into one of your router or AP's LAN ports, give it an IP, and then simply point the router or AP's in it's direction. The thing probably could be sold for like $50. (DWL-2210AP is $250, with built-in RADIUS server and radios.)
...but I guess that would make sense, so I'll be dragging an old computer up from the basement..