Something that I have used since the start of our adventures is a rule that stuns characters that take heavy damage.
If a character looses more wounds from a single hit (after reductions for toughness and armour) than double the characters toughness bonus then they are stunned for one round.
E.g. Mack the ganger (TB 3) is hit by a lasgun fo 10 damage to an unarmoured location, as he suffered 7 damage (10-3) he is stunned for a turn. If it had been a laspistol he would only have suffered 6 wounds and would not have been stunned.
We've used this rule so long we bearly notice but it's very useful for fighting hordes of faceless spods and makes it slightly better to spread damage rather than needing to concentrate fire on each till they are dead. Which of course makes the skill Iron Jaw more worthwhile.