Here's a few of my favorites..
Champions League:
Zidane vs. Ajax in 97
Nedved vs. Real Madrid in 2003
Del Piero vs. Real Madrid in 2008 at Olimpico (including Amoooori's assist)
Del Piero vs. Monaco in 1998 (both the volley and FK)
Conte vs. Man Utd. in 1999 (for such a long time that goal seemed so crucial)
Zalayeta vs. Real Madrid in 2005
Iaquinta vs. Chelsea in 2009 (just a really good goal, great skill from both Iaq and Trez)
Serie A:
Zidane vs. Reggina in 2000
Trezeguet vs. Milan in 2005 (DP assist

)
Del Piero vs. Inter in 2006
Trezeguet vs. Roma in 2007 (first goal against a big team after promotion)
Del Piero vs. Atalanta in 2012
+ all the goals from the 1-6 win against Milan from 1997. Had the game on video tape and watched it like crazy when I was a kid.