Click Mazes is an amazing site jam-packed with puzzles in applet form. These are interactive mazes that are suprisingly challenging: a first look tricks you with the simplicity of the layout into believing that solving the maze will also be simple. Wrong! There's tons of interesting puzzles here, a quick visit won't be enough.
PS: This is one of those pots of gold at the end of the rainbow; in this case the rainbow was this chain of surfed pages: Kevin Altis' Radio Weblog to the PythonCard Life sample to Alan Hensel's Life pages to Dean Hickerson's Life pages to Click Mazes' Maze of Life. Whew!