The Battle of B-R5RB - Eve Online
Eve Online is a special game. One must be a devoted member to spreadsheets to play it efficiently and it's one of the only games that battles are tallied in actual currency as it's a mixture of pay-to-play and free-to-play styles which allow actual currency to be used to increase virtual currency to buy better ships and gear.
The Battle of B-R5RB is one of the most costly battles in video game history. Thousands of players gathered together to fight in one of the most epic space battles one can possibly have in a current video game. The end result was over $330,000 dollars in lost ships and supplies on both sides.