Bayern Munich is almost certainly the best one. There are a few I wish I had been there.. Alex Young's winner v Spurs 1963, Harvey's goal against West Brom 1970, BMG in the European Cup (had to watch the highlights (I was 9 years old)), 5-4 vs West Brom.
Some other great moments
Andy King's winner 1-0 vs the RS
8-0 v Southampton in the snow
Stuffing Leeds
Latchford's 30th
Duncan McKenzie's run across the pitch against Stoke
3-0 vs RS (son's first Derby)
1985 and 1987 title winning seasons (especially the QPR game where we did win the title and the first half against West Ham in 1987 when we won 4-0)
Tony Hibbert's goal!!!
Clarke's winner to end the RS unbeaten run
4-4 vs The RS and then the 2nd replay when Dave Watson netted the winner.
2-1 comeback win vs RS to lift us off the bottom of the table early 90s
Europa wins including Larissa, Zenit and Fiorentina (the last one a bittersweet night)
Tic Tac Gosling's winner (in fact any win over that lot)
2-0 win over Villa LC Semi
Beating Ipswich 2-1 FAC QF (weeks after the 0-4 loss against them in the Cushion Throwing Finale)
Saints 1-0 AET Cup replay
Varadi's winner in the Pie Derby Cup tie
First game with my son (I know it was a lousy 0-0 draw early 90s but it's still a special moment)
Does being one of the 9,080 at the Coventry cup tie (2-1 comeback win, 1983-4) count - stood on Gwladys Street?