One on top of any other:
Tsunade vs. Tendou
Kishimoto apparently wanted her to fight Tendou on top of the Hokage building and for her to be the first one landing a punch on Pain's main body, but his editor denied the idea as anticlimatic and wanted Naruto to be the first.
Revenge and all, Pain pissed at Tsunade's front door way harder than Naruto's, him devastating Konoha and telling Tsunade it was justice, this would've been a perfect stand for her as Hokage and also a nice way to show her prime skills (since she was rusted from not fighting for long in part 1). Tsunade punching in Tendou's face would've been quite the satisfaction.
Other than that, any prime Orochimaru fight. Also would've loved Kishi drawing a fictional Itachi vs. Pain.