Warheads ain't nothing. Get those little gumballs that are encrusted with the sour crystals, they are the real deal. They are HARDCORE CANDY.
Leaving one in contact with the inside of your cheek or lip too long will leave a red spot, and your tongue will be torn up by the combination of coarse surface and acidic coating. Seek them out at mall candy stores like "Candy Express" which deal in candy by the bulk (kind where you scoop up and weigh candy in a bag). I don't know why me and my friends ate so many of these punishing things as teens; I guess it was a macho thing.
Sour Skittle are also no joke, but nowhere near those gumballs. For flavor, I dig the old standby, Sour Patch Kids.