I'm sure there are a few but the one that sticks in my mind was the UEFA cup game against Barry Town.
From my memory the 'You're only Sheep Shagging Bastards' song started from both sets of fans, ultimately changing to the whole stadium singing "We're only Sheep Shagging Bastards". Hilarious!
Can't remember much else from that game - only we won - thank god!
Must be loads of things like that that I've missed....