I like Ghost Hunters because they go in to debunk rather than prove.  Ghost Hunters International is pretty comparable but with all the annoying people that left the original Ghost Hunters.  Paranormal State is pretty good.  I'm not a big fan of the one (I'm drawing a blank on the show's title rigt now) with the three guys who lock themselves in somewhere overnight...they ALWAYS find something and I think that's very suspicious.  There's no way you're always going to find a "ghost" when you go for one night.