My Longest marathon WITHOUT sleeping or taking a break at all was WoW, Basically, my roomate dared me to do it, becuase id been trying to get my guy to 80 for a while, and I was only about 3 levels away...so we went out, bought a bunch of 'Burns' and 'Red Bull' 4 six packs of beer, and then We just played away (He slept, but still played alot) So I played for 24 hours without sleeping and won the bet...And yes I know, not everyone likes wow, But i Still think its da shit (In a good way)

other than that, I did a WEEKLONG marathon of the halo series on legendary with the same guy, (1, 2 and 3) with some matchmaking tossed in.