I went to Woodstock 1999 and it got pretty insane. People were bleeding, equipment towers were brought down, everything was on fire, trailers with refrigeration tanks were exploding and then the state troopers rushed in and starting mowing people down. I saw a state trooper in a Jeep Cherokee hit a guy. It was just nuts. I saw some great shows though.
Best festival I've been to was Roskilde 98. Sabbath w/ Ozzy, Iggy Pop, Deftones, Sonic Youth, Beastie Boys, Rammstein, Slayer, Bob Dylan, Buddy Guy, Misfits and more.