League of Legends

League of Legends has to be one of the best of best web games I've run across. Choose from one of the more than 40 champions and work with a team to conquer the enemy base. 5vs5 teams go up against one another for a battle to the death while earning xp and points to unlock more abilities and talents. I just have one word to say FUN. Sign up and play the game here

ARMOR WARS

Strategy + cards + multiplayer = Armor Wars! The spiritual sequel to Arcomage/Castle Wars, build your decks and beat up your friends. As you play, unlock new cards and heroes in the Shop.

Kongai

Kongai is a multiplayer collectible card game only available at Kongregate. You can earn more cards by completing challenges in other flash games on the site. Play Vs. Man or Vs Machine (cpu). Ranked play is available to keep your stats. G0 try it now.

Dinowaurs

Destroy real enemy dinos online in real-time and battle your way to the top of the rankings. Be the best dino you can be in all of Pangaea!

Armor Wars

Strategy + cards + multiplayer = Armor Wars! The spiritual sequel to Arcomage/Castle Wars, build your decks and beat up your friends. As you play, unlock new cards and heroes in the Shop.

MInions

I found this interesting multiplayer game over at Kongregate. Minions is a team based head to head assault game. There are...

Several units to pick from each with 3 unique skills that you upgrade threw out the battle. Choose from 1 on 1 up to 6 on 6.