Based on the goofy sounding name, the goofy looking logo and the fact that it was Disney, I had assumed Phineas and Ferb was one of their preschool type programs. Apparently not: it looks like it has general audience or at least general kids appeal. Thanks for making me actually look it up guys.
Matt Wilson's High Score has been mentioned but not the incredible, much longer and more polished series of web toons that spun off from it: "Bonus Stage"!
Bonus Stage has crappy animation but incredible writing and voice acting. It's basically a hipster mashup of all the best parts of Homestar Runner and the Rocky & Bullwinkle Show because of it's excellent writing and numerous pop culture references.
Original Flash version:
http://bonusstage.keenspot.com/YouTube conversions:
http://www.youtube.com/user/BSMattW