A vBulletin forum I go on has an extensive arcade mod for it. I've found a phpBB 3 version and implemented it into my (albeit dead) forum just to have a muck around with it and I love it.
I think it will be cool to compete for high scores with each other. It has a leaderboard built into it which is really cool.
http://www.phpbb.com/community/viewtopi ... 0&t=685225
This one is my favourite game right now.
There are a ton of games available here. Registration is required but it's free.
The link to the TOP test arcade is here
http://www.c4family.com/toparcade