Accel World
Kami nomi zo Shiru Sekai (About dating sims)
Sword Art Online
Gun Gale Online (Not yet aired)
.hack/ / Series
Log Horizon
No Game No Life (Currently Airing)
Mondaiji-tachi ga Isekai kara Kuru Sou Desu yo?
The best thing is Sword Art Online, it's is literally based on a game, and takes place in one, haha.
posted over a year ago
SAO isn't based on a game, the games have all come after the anime, which was based on the original manga and light novel series. But you are right, a majority of the series does take place in a game :)
Btooom!! and Ragnarok: The Animation are two that haven't been mentioned. (I have not watched Ragnarok myself, but have heard it is based off a video game and has V.G. terminology)