One's my mind has thought up:
Doctor Whooves saying something like "Don't mess with important dates!" As he scribbles something in a history book.
Pinkemina Pie with the caption "Always use the proper ingredients!"
Rarity saying "Keep your sleeves clean - always look fabulous!"
Twilight: "If the problem can't be solved with Science, it's Pinkie Pie." (Can't think of a good one other than Pinks, so that one could use some help)
Derpy: "Eating in the lab isn't fun if you end up like me!" *Wall-eyed*
Trixie: "The only thing as Great and Powerful as me is an Atom Bomb! At least I'm beautiful!"
Cheerilee: "There's always a chance to learn something new! If you mix two chemicals, what will you brew?"
Zecora: "Use ingredients at their exact measure, Lest you leave here on a stretcher."
Anyone else got some good ideas?