Haven't done it in a while, but the Trifecta Combo (Weed, Shrooms, Alcohol) is always fun.
There's a fine line between having fun and being an addict, however, so I definately do not advocate anything above the level of 'shrooms. By this, I mean the drugs that are potentially life destroyers (Coke, Heroin, etc) should be avoided. I mean, I've tried opium (addicting, I know), I've tried LSD, I've done the RoboBuzz (DXM), but I wont touch anything else.
My philosphy on the whole thing is basically that I'll try anything that doesn't have the potential to kill me or addict me. It's not a perfect rule, but it's a decent one.