A mini game from \"our\" world like: chess, poker, etc... Would be great too, and ofcource a game invented for the game itself.
But games which everyone knows will be played faster, so like chess that would be played in a tavern pretty quick because (almost) everyone knows the game already. And the rules are set, so no comming up with ideas \"just\" program the game ingame

(just, right, lot of work )
And the card game that is being invented atm on the forums, that one should be ingame too, but that will take longer to make offcource. And I like that idea too