Here are some of the house rules we've used so far.
Messy Death: Inspired by the WW2 skirmish game 'Operation Overlord', we decided that when a model killed by a high impact weapon (Str 7+) goes out of action, all friendly models within 6" (rather than the normal 2") should take a Leadership test. Furthermore, that model doesn't get to roll on the Serious Injuries table after the game - he's dead Jim!
Pinned: we reckon a target that's just ducked for cover would be harder to hit. Therefore, shooting at a Pinned model is at a further -1 to hit.