In 2004, the Penny Arcade Expo started in Bellevue, Washington. Since that time it has expanded to PAX East in Boston, PAX South in San Antonio, PAX West and PAX Dev in Seattle, and even PAX Aus in Melbourne, Australia.
With massive attendance numbers and a focus on gaming, PAX is one of the largest gaming conventions around. And a large convention means large amounts of cosplayers. From League of Legends champions, to Mortal Kombat, to Pokemon, all manner of costumes can be found at one of the PAX events. Again, tickets sell out quickly -- so get ready to queue as soon as the site goes live.