She may be perpetually eight years old, but Lisa is the voice of reason in Matt Groening's The Simpsons.
Off the top of my head, I can think of a few examples of Lisa's scepticism in action - the most obvious of which is the episode The Springfield Files (starring the voices of The X-Files stars David Duchovny and Gillian Anderson, as well as Leonard Nimoy). I'll share with you the wonderful opening line delivered by Mr Nimoy:
"Hello, I'm Leonard Nimoy. The following tale of alien encounters is true. And by true, I mean false. It's all lies - but they're entertaining lies; and in the end, isn't that the real truth? The answer, is no.
That really sets the scene for the whole episode. The basic storyline is that Homer gets tanked up at Moe's Tavern and has to walk home - through the woods. He gets spooked by various things along the way, and finally comes across a glowing, willowy figure who approaches him and tells him not to be afraid.
Everyone is sceptical of his story at first, especially Lisa who quotes odds from "Junior Skeptic Magazine" of alien life visiting Earth. Finally however, they manage to capture shaky, hazy video footage of the "alien" which, despite the poor quality, snares the attention of the entire town. Meanwhile, little Lisa insists "There must be a more logical explanation."
And indeed there is. As all the town stare aghast at the glowing figure (and threaten to break its legs), Lisa steps forward with a flashlight and cuts through the glow to reveal a certain Montgomery Burns. He's high on painkillers and had a vocal chord scraping; the glow comes from a lifetime of working in the nuclear power plant. Occam's Razor in action.
This is only one example of many, of course; mysteries abound in The Simpsons, and with few (if any) exceptions, Lisa is the voice of logic and reason. A true skepchick.