Ratskinner
Adventurer
For example, if you are willing to assume that a typical adventuring day would consist of 4 encounters of 5 rounds each, and that an AEDU character would use 4 encounter powers and 1 daily power over those 20 rounds, you could have a "encounter" power level effect trigger whenever the character makes an attack roll and gets a score of 16-19 and a "daily" power level effect trigger whenever he gets a natural 20.
Y'know I slept on this idea and it reminded me of something from FATE (some versions of it, anyway):
If your effort is higher than the number required,
you get shifts equal to the difference between your roll
and the number. You can spend shifts on special effects
enhancing your action, making it faster, better, hurting the
target more, discovering more about something, and so on.
For example, if your effort is 5 and the difficulty is Good (+3),
then you’ve succeeded with 2 shifts.
A similar thing in DnD would be comparing your attack roll to the AC needed to hit. Every "step" of AC that you hit, but didn't need would get you a "shift". You could spend these shifts on doing the tactical aspects beyond "I attack". (So if the target has AC 15 and you could have hit AC 18, you'd get three "shifts" to spend.) I would presume that Fighters and other melee types would have special/bonus/unique maneuvers to which non-fighters wouldn't have access. Monsters could have short lists of "specials" that they could buy with shifts (Swallowed Whole, Poisoned, Entagled, etc.)
Examples:
Bull Rush (3 shifts) - You push your opponent 5 ft. back. This only works on opponents who are one size category larger than you or smaller.
Disarm (5 shifts) - You knock your opponent's weapon from his grasp.
Greater Disarm (8 shifts) - You disarm your opponent. You may choose to take his weapon.
Sidestep (2 shifts) - You may shift 10 ft. without provoking an Opportunity Attack.
The DM would only need a short list of the generic ones, and those available for each monster/NPC. For that matter, a group might decide to only use the special maneuvers on the players' side, or for special monsters only. I suppose the impact and occurrence of the maneuvers could be (relatively) easily dialed down by adding one or two to the costs, or by just doubling the costs of the maneuvers. Feats or other tweaks could alter the costs for certain maneuvers.
The super-basic version would be "If the fighter's attack greatly exceeds the AC he needed to hit, he may add some extra movement or special effect to his attack."