In another note to The Ocean Group, the actors who played the characters in the series were also voicing a lot of characters from the My Little Pony series, starting with My Little Pony Tales and continuing to My Little Pony Friendship Is Magic. So we have:
Sarah is an insane version of G3/Core 7 Pinkie Pie. Heck, even her voice matches Pinkie perfectly when she screams in A Very Minty Christmas.
Ed is Soarin'. This explains his rather air-headed personality in Season 1 Episode 26. Mmmm.....Pie.
In Croatian, Edd (violin video at 0:06) sounds almost exactly like [1]SpongeBob. Both are voiced by Ronald Zlabur.
The middle names of the titular heros are as follows:
Ed: Horace
Edd: Marion
Eddy: Skipper
In the episode To Sir With Ed, we see Nazz stand by the stairs at one point. During this scene, we see a picture of what looks like Eddy standing next to someone...his brother?
In the movie, when Sarah tries to escape, Lee's hair gets pulled up and she has three eyes. O.O.
In Ed's room the titles of the books shoved in random places were homages to H.P. Lovecraft ("Beneath The Mattress of Madness"), Robert A. Heinlein ("Wet Planet") and other SF/Fantasy authors.
This was the last major cartoon to be entirely hand drawn. In 2004, the animators were forced to use digital coloring, but all outlines were still done by hand.