1) Final Fantasy X:
You dodged lightning 100 times (it took about 40 minutes of steady pressing X) you were reward a nice sword for Tidus.
2) World of Warcraft
You raised a pet dragon, trained it, educated it. (it took 3 months) You were granted a mount or companion pet.
Would be fun to have those bonus rewards for small bits in the game that are of the main game but more of a minigame or just that extra for the fans who want everything.
Mini-games would be fantastic.
1) World of Warcraft went up a level of amazing when in their 2nd expansion, they included a repeatable daily quest that involved a Simon Says type of mini game.
2) Have you tried Warframe? New mmo where you open doors, you have to hack the computer system and it's a puzzle involving either tetris style or simple mathematics.
To be part of your future.