attacks of opportunity

Ooh. Good topic.

Fate Points
Games: Savage Worlds (bennies), Spirit of the Century (aspects), Star Wars (Force points), Trollbabe (re-rolls)

I think most games that use Fortune benefit from a Fortune-adjusting resource of some kind to allow re-rolls, one-time dice bonuses, or something similar. This layer of resource management adds decision-making and value judgments into the system, keeping it from being an exercise in random number generation.

Keys
Game: The Shadow of Yesterday

Players decide what activities cause their characters to gain long-term effectiveness. This is one of the most impressive player-empowering tools, and it doesn't involve any strangeness like narration trading or GM-lessness so it can be added to most any game under the sun.

Tech Burner
Games: Burning Empires
Burning tech, particularly the use of color, is awesome cool. TSOY also allows this in a way simply by being so open-ended as regards to equipment.

Also Keys.

Lifepaths
Games: Burning Wheel
OK, I admit it. I love fiddly lifepath-based character creation trees. So sue me.

Narration of Failure/Success

I don't know which game I saw it in first, so I won't credit any. I love the idea of players narrating how they fail and GMs narrating how they succeed. I use it in DnD and similar games for all the non-combat situations like diplomacy checks, bluff, and all that stuff.

To continue strip mining from TSOY's greatness:

Gift Dice. Keeps the players together, gets you out of annoying narrative situations, leads to fun dynamics with gift dice bartering.

There should be something like that in every game, pretty much.

-milo