If I were looking to annoy the Aussies out there I'd say Jonny's drop goal in the 2003 RUWC final!
Really though, as a lifelong Gooner it has to be Mickey Thomas's goal when we dicked the Scousers 2-0 back in '89 to claim the old Div 1 title for the first time in my lifetime.
Linford Christie's win in the 100m at the Barca games was pretty special. Shame the dill had to tarnish it by being done for drugs ages after.
From a cricketing perspective it has to be the Lord's test against The Windies in 2000. We'd conceded a 100+ deficit from the first innings, but then Caddick, Cork & Goughie skittled them out for 50-odd in their second. Dom Cork saw us to victory with as good a 33 not out as you're likely to see when we'd been eight down with (about) thirty still needed. Ambrose & Walsh were steaming in but Dom stood firm with (I think) Goughie at the other end. Back then it wasn't often we used to guts out results.