Core class-wise, I don't use the monk, almost regardless of the campaign I'm running. Even if it's a campaign setting where they're included, I'll probably drop them. If the world is pseudo-European, which most are, the monk gets the boot. I extend my cross-cultural acceptability to around the Middle East. Past that, I'm not much for mystics who can put their fist through plate mail and walk across rice paper without leaving a trace. If I'm running a more Asiatic-influenced game, that changes, but that's a rarity.
Individual campaigns differ beyond that. I tend to go with games where magic-users are given a suspicious glance or worse, whether it be in my own home-brewed ones or those of a prepackaged variety (Midnight, Ravenloft), but I make it a point to warn the characters about any troubles they may have ahead of time.
I also tend not to use many traps, diminishing some of the effectiveness of the rogue, and don't use many dungeons, either, which can hurt some classes, but none of those are attempts at dissuading those classes from being played or the like.
While not a core class, games where I allow psionics are the exception, not the rule. Elements that smack of science fiction tend not to make their way into my games.
But, as I said; monk is really the only core class I disallow.