I find the best AP to end a bad stimulant trip is Seroquel, it kills off both the paranoid thoughts and agitation, and has you off to sleep pretty quickly; I've used it twice when taking EPH and in some ways it's better than benzos for that purpose.
More difficult is if you need to kill a stim but still be able to function afterwards and can't afford to go to sleep. I've heard that Abilify at a high dose can work, although I've never tried that personally.