I think I've found my groove for now with the sort of things I want to make - little practice projects that demonstrate some physics and/or demonstrate a numerical technique. Also amusing my children for a few minutes is important.
Anyway my latest thing has physics (gravity) and implements a variable sized grid to show the gravitional potential (and looks quite pretty I think). Trouble is there's no actual gameplay, you just click on the grid and add a planet.
Go to http://www.moonsch.com and go to the Games Links, it's at the bottom called Planets, Pot Noodle.