Sardines

This is also known as "Reverse Hide and Seek." It's an ideal game for a big group, more so than traditional Hide and Seek (in which everyone is hiding at the same time and know where their friends are, making it really lame when they all find each other once they're found).

To play Sardines, everyone starts in one room or location. One person is selected to go and hide, while everyone else stays and counts to 100 (or whatever number they agree to with the "hider"). When they reach 100, everyone splits up to search for the person who is hidden. If anyone finds him/her, they hide with him/her. This continues until everyone is hidden except for one person who is still looking for the original hider (and everyone else who has joined him/her). The game can get pretty silly if 6 people are trying to fit under the same table or in the same closet.

This game also works outdoors, so long as the area is limited (such as a park or yard).