Hmmm, good question. Outside of the Muppets.... I'd have to say Lisa Simpson. We're both intelligent, Buddhist vegetarian activist chicks who often feel like no one understands us. Comic Book Guy, a little bit as well, because we're both comic book nerds who are uber-sarcastic and obsessed with being right.
Also, when I was in high school, some kid who bugged me all the time in my English class said I was like Daria (from the show of the same name), because my responses when he annoyed me were usually deadpan and sarcastic.