Ferb's full name is possibly revealed in the episode The Beak. At the beginning, when Phineas and Ferb are standing at the top of The Edge of Insanity Kiss Your Butt Goodbye Gravity's A Stone Cold Sucker Nightmare Rail Skate TrackObstacle Course of Doom, they accidentally drop the skateboard down the rail and watch the mayhem ensue. At about 29 seconds into the clip, Phineas says "Well Ferbutch(?), unfortunately there's only one way down." Either this is a nickname or this is Ferb's actual full name.