I've got an idea. Let's just put a freakin' cannon to their heads. No pain (at least not for more than a milisecond). Also none of the nasty "he's brain dead but he's still got a pulse" crap. If there's no brain (or head) left, there's no pulse. Cheaper than the electric bill. Not as complicated as the 3-drug method. Not as inhumane as hanging. More certain than any of the above. Perpetrator's witnesses might be a little upset, but nobody's forcing them to be there...
It's Florida - you'd think they'd just starve and dehydrate them to death. Oops, I forgot, they only do that to innocents.