Alexi uses a Crate 2x12 120 watt combo on the FUCKING EXTREME channel. He also uses 2 Ibanez tube screamers at once in conjunction with a Boss Mega-Distortion and a Morley Wah through the FX Loop.
There are so many threads explaining Alexi's setup that it doesn't need to be a Sticky... It's probably on the front page of the forum 4 times right now.