Sonic the Hedgehog had a pretty healthy life outside of the games. I enjoyed the comic books and the original Saturday morning cartoon. However, Sonic has had so many reincarnations and different origins, even in just the games by themselves, that it's pretty much impossible to say what is canon anymore.
The Portal series doesn't have much to offer outside of the games, but there was a really good comic book that not only bridged
Portal to
Portal 2, but also filled in some gaps left by
Portal 2 about how GlaDOS came to control Aperture Science.
Of course, back in the days of Atari, going beyond the game was simply a matter of picking up the instruction manual. Would you have known you were representing the Zardonians in their interplanetary fight against Krytol in
Missile Command? Or that you were helping Oliver in his battle against the evil
Centipede (or maybe the centipede is just a hypnotized friend, if you chose to believe the comic book instead)? Or that
Defender,
Berzerk,
Star Raiders,
Phoenix and
Galaxian all shared a common backstory... somehow... maybe?
Edited by FujiSkunk, Wed Feb 22, 2012 1:42 PM.