Lisa Marie Simpson, voiced by Yeardley Smith, is Homer and Marge's oldest duaghter and the middle child on The Simpsons.  Lisa is very intelligent, plays the saxophone, is a vegetarian, Buddhist, and definitely a bit of a young political activist.  She's basically the complete opposite of her brother, Bart.

Lisa Simpson Quotes

Lisa: Dad, I think he's an ivory dealer! His boots are ivory, his hat is ivory, and I'm pretty sure that check is ivory.
Homer: Lisa, a guy who's got lots of ivory is less likely to hurt Stampy than a guy whose ivory supplies are low.

Bart and Lisa: (Singing dull) Hot dogs, Armour Hot Dogs.
Grampa: Sing it like you mean it!
(Grampa plays harmonica and the kids sing it with style.)
Bart and Lisa: What kind of kids eat Armour Hot Dogs?
Bart: Fat kids.
Lisa: Skinny kids.
Bart: Kids who climb on rocks.
Lisa: Tough kids.
Bart: Sissy kids.
Milhouse: (Sticks head from the window.) Even kids with chicken pox love--
Family: Hot dogs, Armour Hot Dogs.
(Grampa stops playing harmonica.) The dogs kids love to bite!
Lisa: Doesn't this family know any songs that aren't commercials?
(Everyone except Lisa starts singing the "Chicken Tonight" jingle.)

The Simpsons Quotes

Principal Skinner: You're not supposed to be able to get outside our network.
Nelson: You shouldn't have made your password, "password".
Principal Skinner: It was the name of the street I grew up on, Password Drive.

Homer: (Wearing glasses) The sum of the square roots of any two sides of an isosceles triangle is equal to the square root of the remaining side!
Man: (From inside a bathroom stall.) That's a right triangle, you idiot!
Homer: D'oh!