The Dollar General in Rosewood, Florida (Site of the Rosewood Massacre)
The Dollar General was built in 2005, but in 1923 the Rosewood Massacre occurred (For the full story, see the wikipedia page: http://en.wikipedia.org/wiki/Rosewood_massacre)
I used to work in the Dollar General and myself and all my coworkers have experienced SOMETHING. There's AT LEAST two spirits there. There's one who stays up towards the front of the store we lovingly refer to as "George". He just kinda plays around. Moves things around, makes the lights flicker, you hear cereal boxes fall (and hear the cereal rattle around when it falls) when you're on the next aisle over and when you go to pick it up, nothing's there. You'll put something in a new place and he'll move it back to where it was and etc. The other spirit(s) stays in the back of the store and has a very NEGATIVE feeling. You feel breathing on you, hear voices, see shadowy figures, and on more than one occasion I've found drops of what appear to be blood on the floor AFTER I've swept and mopped the store AFTER HOURS (only me and my boss in the store, and she would stay up at the front of the store).
Also I'd like to say as a Cedar Key resident, I wouldn't say the WHOLE island is haunted. there are a few presences here and there, but not "all businesses have at least one spirit".