Non-plugin based games are preferred, I'd ideally like to have the Games Lobby up during server maintenance/update times (like the upcoming update to 1.7). I don't want to have to maintain plugins between versions for these mini-games, along with the plugins needed on the main server. However, I'm not against having a few select OMGtotallyworthit plugin-based games in the list
Games which need to be reset between rounds are not a problem, we have a few maps like that which I have automatically reset when the server restarts. The only problem arises where a game does not have an official end, some are set up for the players to decide amongst themselves who the real winners are, and when to end the game. Ideally there should be a system in the map which activates redstone on-win, like in the case of hotfoot where command blocks could be used to detect how many players are left in the arena. If there isn't a system built into the map, we could look at adapting the map to work it in. Otherwise, some of the games will require an operator to run the game, and decide when to end the game (stop the server to have it reset). We have a few games which require an operator already (but I hope to automate them in future)