As my shop is very small there's not a lot of room for massive tournaments, but I want to attract some gaming attention and have put in a small round gaming table, like this:
As you can see there's not a heck of a lot of space.
So here's my idea. Every local gaming club selects a player. That player comes to the shop and matches his wits in a small three-room dungeon with other selected players from other clubs, all with pregenerated character so that they balance. The character surviving the dungeon wins. If more than one survives, the one with the most XP wins. If it's a tie - they duel! This is also the case if they all die. The winner gets a free game for their club and a little plastic trophy with 'woohoo!' inscribed on it, and a picture on the shop wall. The games are bi-monthly.
It's small and needs some little house rules, and I have no idea what system to use, but it would be a lot of fun.