The Planck Temperature, 10^32 degrees K is the hottest possible temperature, using the Standard Model.

That's so trippy, a little summary: at 10^10 degrees, particles approach the speed of light, but as we all know, you can't reach the speed of light, you just get more and more massive. So, at 10^32 degrees, each particle of matter becomes so massive, it turns into a black hole. Trip-p-y!