Cellular Automata Using Small Boards
"interesting" is very subjective.

You could try Brian's Brain or Brian's Seeds, both of which I find interesting.
http://en.wikipedia.org/wiki/Seeds_%28cellular_automaton%29

While they are designed for an infinite plane, you could wrap your 4x10 grid at the top and bottom presenting a theoretical sphere instead of a plane.

As a interesting thought, you could start with Langton's ant and then add a swarm to the ant, then chose a random element of the swarm to take over control for the next X iterations.