Currently there's 200+ io games, some're already down. My favourite is Glor.io, I would advise http://titotu.io as a source of most recent io games. Also liked recent spinz.io game. Btw I'm not big fan of agar.io, the game has tons of clones and most of them're awful...
.io games are dead,just like this wiki. KokoroTabi is the only active contributir.
You must try the wilds game: http://www.bibib.net/wilds-io-gd/
^ its me pitrioptixiop still
There are over 1000+ .io games aafter the initial release of agar.io