MUFON
The Mutual U.F.O. Network. A central location to add or view U.F.O. reports. The site also provides a lot of information along with valuable resources as well as links to various state specific sites.
N.U.F.O.R.C.
National U.F.O. Reporting Center, a site very similar to M.U.F.O.N., though they do not investigate.
C.U.F.O.S.
Center for U.F.O. Studies. Organization started by J. Allen Hynek.
U.F.O. Research Center
Investigative and news site into the U.F.O. phenomenon.
U.F.O. Reports.com
Displays media related to U.F.O. sightings.
U.F.O. Evidence.org
U.F.O. Evidence, photographs and research into the U.F.O. phenomenon.
U.F.O. Casebook
Site that displays current sightings all over the world.
U.F.O. Stalker
United States map showing current UFO sightings. Does not seem to be 100% accurate.
MADAR
Get a MADAR unit and receive notices when UFOs are in the area.
Missouri MUFON