Viva Rivaldo said:
Lots of good ones mentioned already...
7-1 against Roma was great, the 1999 final vs Bayern, 6-1 against Arse, 4-3 derby last season, our comebacks against spurs (5-2, 5-3) far too many to list.
United 4-3 Madrid was amazing too. The best ever opposition player performance I've seen at Old Trafford, fat Ronaldo at his best, superb hat-trick. You just know when you're outclassed.
For neutral games, I'd say the Liverpool-Arsenal 4-4 two years ago, the 4-4 in the CL between Liverpool and Chelsea, the 2005 CL final, 5-0 El Classico this season; amazing football.
3-2 against Villa when Macheda scored as well, doubt I've ever wanted to kiss a 17 year old Italian lad as much as I did that day...hmm
Read all of this thinking... surely this is a piss take, then I remembered that there's an insurmountable amount of rags on bluemoon :)
For me, City 4 - 3 Spurs, it's the match that made me a city fan.
Then there's the Liverpool AC Milan Cup Final, I was on the edge of my seat for the whole second half of that match, the kind of incredible match where you will on a team you don't even like to win because they are doing something incredible.
Inter 4-3 Spurs earlier on this season in the Champions League was pretty brilliant aswell, wanted them to score a 4th so much.
Some other notable mentions of matches I really enjoyed, Germany Argentina at the 2006 WC, Turkey v Brazil at the 2002 WC, Spain v South Korea and Italy v South Korea at the 2002 WC and Ghana Uruguay at last years WC. The 2-2 draw between Sweden and Denmark(?) in Euro 2004 that knocked Italy out was pretty great aswell because it was the only result that would see both teams go through and Italy out.