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

Anya: (in a girls voice) "Dear Lisa, as write this, I am very sad. Our president has been overthrown...(man's voice) and replaced by the benevolent General Krull! All hail Krull, and his glorious new regime! Sincerely, little girl."
Lisa: (groans)

Bart: Dad! Lisa's making me see things from both sides again!
Homer: Lisa, I warned you about that!
Lisa: Shouldn't Bart have all the information he needs to make an informed decision?
Homer: Now you're doing it to me, aww...

The Simpsons Quotes

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!

Homer: Aw, twenty dollars? I wanted a peanut!
Homer's Brain: Twenty dollars can buy many peanuts.
Homer: Explain how!
Homer's Brain: Money can be exchanged for goods and services.