Sookie is telepathic. She almost always has some level of mental blocking up so that she won't hear everyone's thoughts, but she can hear most people if she doesn't.

For a full list of who she can/can't read, go here (http://justwantsquiet.livejournal.com/1000.html#cutid4). Otherwise, she can't hear vampires no matter what, but most supernatural beings give her some trouble, and anyone with similar powers should be able to tell if she pokes around.