Jackson-Griffin is the most memorable one for me. Probably not the best fight ever (Allthough, it was a candidate for that year's FOTY) but it meant a lot to me, since Griffin and Rampage are 2 of my 3 die-hard favorites.
Also, the fact that it was coming off that great season of TUF7, which really helped building it up.
That was the only fight in which I stood the entire 5 rounds.
2 runner-ups probably are Rampage and GSP gettin sweet revenge on Wand and Angry Midget. Those fights were fantastic for me.