Here are a bunch of the options for on-line contests:

http://www.xcontest.org/national (probably the easiest if you want to set up
a regional or national contest)

http://www.xccomp.org/module.php?id=1&date=20100219 (a number of contests
are run here)

http://www.onlinecontest.org/olc-2.0/para/plainJsp.html?prefix_jsp=rules#phg,phgleague
(This is the oldest one.)

http://www.leonardoxc.net/support/viewtopic.php?t=168 (if you want a
separate contest you set up your own server)

http://www.fai.org/hang_gliding/WXC  (a collector for other contests).