The longest I've ever stayed up is two days straight at an animu convention. I'll stay up until 9 or 10 AM, on occasion... 'cause I'm crazy like that @u@
Lately I've gone lots of days without any sleep at all but I think the longest I've stayed awake was for like four days straight just earlier this month.
I was up for four days too once after experiencing my first night terror. I think the longest before that was three days, but that was because I was stupidly experimenting with ways to stay awake longer with a friend of mine. Stay safe, kids.
Somewhere around 48 hours. Either from me playing games too much and trying to fix my sleeping pattern for school again, staying up to finish work I should have done earlier, or times where I have got back from trips in largely different timezones and wanted to fix my sleeping pattern again.
I've probably lost count of the longest I've been up... Since in college I stayed up til morning doing plates. There were even months when I had no proper sleep.