Mary Elizabeth Ellis is best known for portraying "The Waitress" on It's Always Sunny in Philadelphia. I think she's very sexy, if you don't see her as a sexy girl, that's because you're a girl, but she's very hot in my opinion.
She is hot in a very nontraditional sense. Its hard to pinpoint why, but she is hot. I mean, if charlie married her RL, when he could have his pick of many different women, that should tell you something.