This past weekend, a friend of mine had their Stag and Doe.
It's a pretty common thing around here, but I gather it isn't elsewhere, so I'll try to explain. It's basically a big party put on by the future bride and groom, with the main goal of raising money for the wedding.
Usually you rent out a hall or something, and sell tickets to as many people as possible. This is also another way for friends/family to be involved in th wedding, even if they aren't nessecarily invited to the wedding (to keep the guest lists smaller). The ticket prices cover the cost of the venu, food, and entertainment (dj/band).
Most of the profit is generated by things at the event. They'll usually have silent auctions where you buy raffle tickets for prizes that people have donated. They'll do games as well were you put some money in for each try, and the winners at the end of the night get some kind of prize that's also been donated.
The event itself wasn't all that organized, but went pretty well. Being the best man, I was informed at the event that I would be the master of ceremonies for the night shortly before the event started. They got me a microphone, and I was pretty much left to run the show. I'm not super comfortable with public speaking, but I think it was a success. It looks like I'll be reprising the role of MC for another friend's wedding later in the summer. Should be good times :D.