What are some good interactive computer games?

I want to play a game with my sister, on seperate computers, are there are fun interactive computer games, that we can both play at the same time? maybe against each other, or like a team? or something!!!What are some good interactive computer games?
i have a fun game, but you didn't say that it can't be downloadable so i assume that you can download the game. The game i play alot and is a lot of fun is maplestory, dungeon fighter online, league of legends, and combat arms. The links are in the sources. I know the league of legends is a referral link but it helps me out and it doesn't do anything to you so why not? :) if you choose the referral link, thanks :). The original website clean is leagueoflegends.com . You can find fun games at nexon.net (if you haven't noticed basically 75% of the games i showed you were from nexon)
*EDIT*: Hey thanks so much for using my referral link! My Summoner Name in LoL is xXEric702xX! Add me! Hope we can play together soon ! :)