Seriously, tho, there are so many good ones, gotta list a lot:
My favorite 3:
Orochimaru vs. Saratobi
Rock Lee vs Kimimaro
Rock Lee vs Gaara (which I believe confirmed that any Genin's other than Gaara would have gotten destroyed by Rock Lee, at least at that point in time. Stupid armor of sand and that damn gourd. Rock Lee shoulda ripped that thing off and threw it somewhere
).