A Steam group sounds like a nice idea! I wouldn't mind to have more people to play with.. x:
Some games we (probably) could play together: (some of the ones mentioned before included)
Steam games:
Team Fortress 2 (free, though we'd sorta need a bunch of people)
Spiral Knights (free, 2-4 people at a time in the same group)
Terraria (Varies..)
Worms Reloaded (2-4 people)
Dungeon Defenders (2-4 people)
Magicka (2-4 people)
Monday Night Combat (2-4 people on co-op, max. 12 on team vs. team)
Left 4 Dead/Left 4 Dead 2 (?, I have a un-redeemed copy of 2 but I have no clue about the game itself)
Non-Steam games
League of Legends (Seems like a plenty here play it)
Heroes of Might & Magic III/IV/V (JUST BECAUSE [although the games tend to last really long])
Ragnarok Online (YAY LET'S ALL MAKE NOVICES AND KILL PORINGS AND MORE PORINGS AND MAKE PORING-PORRIDGE)
*Insert-game-here* (Hey, let's all play (game) because in (game) you can do (game-stuff) and we can make (game-things)!)
..and I mostly suggested those games because I already have them all/play them myself.