BYOAC tokens are a community project started in 2004 and have since become an annual tradition. Dave Santoro ('Santoro' in the forums) created these tokens after several previous discussions on the idea didn't get off the ground. The first thread is here: http://forum.arcadecontrols.com/index.php?topic=19172.0 .
The BYOAC tokens are accepted by coin mechanisms found in many arcade machines. Many BYOAC members also include a coin door in their scratchbuilt arcade cabinets and a set of original tokens is a nice addition.
So far they are all .984" (25MM) in diameter, the most common size in the industry. If you have a Bally or Midway coin door you may need to modify your coin slots (see http://forum.arcadecontrols.com/index.php?topic=52277) or get smaller .90" tokens elsewhere. Many, but not all, US Quarter mechanisms can be modified or adjusted to accept .984" tokens. (See http://forum.arcadecontrols.com/index.php?board=1;action=display;threadid=22251)
BYOAC Tokens are avaialble at http://www.arcadetokens.com.
The 2006 coins are currently being designed. The thread can be found in the artwork forum here.