DisplayLink (http://www.displaylink.com/) has posted new Mac OS X
beta drivers for the software that lets you add up to four additional
monitors to any Intel Mac through USB. The new beta (version 1.5) is
compatible with Mac OS X 10.6 (“Snow Leopard”).

With the drivers, even a Mac mini can have four additional monitors
for a total of five. You can manage and configure DisplayLink USB
multi-display technology using the standard Mac OS X System