The Ghost Hunters investigators are members of TAPS: The Atlantic Paranormal Society. They don't charge for the investigation, and look to disprove that there is paranormal activity rather than prove there activity in a certain location.
The show has been on air since 2004, and have had many guest investigators such as Colin Ferguson of Eureka, Joshua Gates of Destination Truth, CM Punk, Elijah Burke, and Mike Mizanin (all from World Wrestling Entertainment).
The show airs every Wednesday night usually starting at 7:00pm EST with 2 old episodes then the new episode at 9:00pm EST. SO tomorrow night!! NEW EPISODE! Ghost Hunters - Next Episode - Rocky Mountain Haunting
Visit their official Syfy page for more details on the show and to watch full episodes. You can also go to the TAPS official page for information on The Atlantic Paranormal Sociey.
p.s. - I got to meet the Ghost Hunters: Grant, Jason, Steve, Tango, and Kris & then Dustin and Joe from Ghost Hunters International at Dragon*Con this year. They were awesome, very down to earth!
Rock on!
~Mo