Types of Reward?

I am interested in learning what different categories of reward mechanics exist in RPGs. I haven't found any threads that address this (my search-fu is weak) -- perhaps someone can point me in the right direction.

Many reward mechanics are expressed in currency that can be spent -- but it's what you spend such currency on that I'm interested in.

Most games seem to reward players with permanent character improvements. Good play earns you increases in your character's abilities.

Many games also reward players with temporary character improvements, like a one-time bonus to a roll.

Rewards in Buffy and Adventure! include one-time moments of increased credibility for introducing elements from Director Stance -- plot twists, features of the setting and so on.

I imagine some Gamist games reward players with points that cannot be spent, but instead serve only to show how well you did in the game.

Do any games reward players with extra spotlight time?

What other kinds of rewards are there?

The reason behind my question is that I'm toying with a Karma-based system design, and I'd like to give players currency to a) override the Karma, and b) serve as some other reward. But I don't want that other reward to increase character effectiveness in any way. I expect the system to handle lots of player-vs-player conflict, and so I don't want any player who hoards currency to cash in on reward b) and become unstoppable.

Thanks for reading -

- Adam C.