Here are some useful links.
Please contribute more.
Interactive Introduction to Graph Theory
Discrete Mathematics Course Website
(Berkeley)
Discrete Mathematics Course Website
(Swedish University)
Discrete Mathematics Course Website
(University of Toronto)
Graph Animations
Graph Theory Tutorials
Discrete Mathematics
(PDF file)
Discrete Mathematics
(Ryerson University)
Another Discrete Mathematics Link
Tarski's World
Tilomino
Tiling with Trominos
(Example of proof by induction)