By far, my favorite character, and he comes up with some good lines, too.
Here is one of them:
Don't fight for a king. Don't fight for his kingdoms. Don't fight for honor, don't fight for glory, don't fight for riches, because you won't get any. This is your city Stannis means to sack. That's your gate he's ramming. If he gets in it will be your house that burns. Your gold he steals, your women he rapes. Those are brave men knocking at our door. Let's go kill them!
Oh, Tyrion!