About 25 hours is my longest, playing Star Wars: Knight of the Old Republic. I literally passed out, so it didn't count. I could've kept going, but like I said, I passed out. xD
I didn't have any caffeine, sugar, or the likes beyond a couple sprites and about a box of Capri-Suns. Try going your longest without that.
I usually play around 60 flash games on weekends and around 100 weekly.
My longest time playing games without sleeping is 25 hours. I woke up, and go straight to the laptop. Didn't even bother to bathe. And I eat light snacks when I'm hungry.
14 hours of FIFA 10 at a mates house is the longest in one time, but I play some flash games during the day maybe 1 or 2 hours .. 14 hours non-stop really messes up your sleeping pattern though D: