There are so many, I can't pick one, but, one that hasn't been given much love on was Paul Pierce's dagger 3 right in LeBron's grill game 5 in Miami.
I was in Santa Monica and a Celtics sports bar watching this, wow!! Everyone went beserk! Great memory of my trip to the US!
http://youtu.be/K_uulujs-MMEdit: I could not get the embed link working, link above.