Liam O'Brien is one of the more recent voice actors. Chances are that if you notice a character who seemsaristocratic orhave noble standing, they'll have this guy voicing them. Most likely characteristics of his voice are an almost-faux British accent or a very laid-back demeanor. And he doesn't differentiate that much--
--"You want any voice differentiation? That's Gaara!"
His real forte seems to be voicing characters who have more than a few screws loose in their head, from the eccentric to thecompletely batshit insane. In fact, this is what shot him to fame when he voiced Gaara inNaruto. He has a knack forAmbiguously Gay characters, and one hell of anEvil Laugh that's present in just about every villain he's ever played.
He's currently[when?] married to fellow voice actressAmy Kincaid (who played Shirley Fenette inCode Geass and Kotone Himekawa inTo Heart), and also does a butt-load of ADR directing (Most notably for the most recent entries in theResident Evil series).