Ideally I'd like an option that will let the players roll dice during combat, give them a meaningful bonus for success (and probably a noticeable, but not crippling, penalty for failing), allow them to get positive circumstance modifiers for good thinking / planning, not slow down the game too much, encourage cool descriptions / action scenes, and that the players will voluntarily attempt, rather than having to force it on them.
Have you looked at the Stunt mechanic from Iron Heroes?