Marauders with Medivac support for against his ground. Get Vikings in the air if he has Colossi or any air units. Ghosts are a mega plus since they have EMP Shot. The Protoss can wave goodbye to their shields.
I have yet to see anyone use the ghosts EMP shot, prolly just because im in lower leagues but dunno, hell i have only seen somone pull the ghost nuke strat like once. once again prolly because of the leagues im in... So anyway how effective is the EMP exactly?
It drains all shields from Protoss. All shields. And it's something like 25/50 energy to use. Throw two or three in your army and you're good to go.
I always go rauder, tank, and vikings when going against protoss. MMM get completely murdered by psi storms all the time. Ghosts usually come in late game when the battles get real intense giving you the huge advantage over your opponent with the EMP.
I would recommend a banshee rush in 2's or 3's, MMM in 1's. The reason is because banshee rush attacks protoss ground effectively as they do not have scanners. You want to make sure they don't have a lot of photon cannons in place as it can destroy this strategy. Don't rely on it too much in 1v1, though. Leaves you highly exposed to a counter attack. For 1v1, Classic MMM with a possible ghost or siege tank will work wonders on protoss infantry, if done appropriately.