Again, this is another one that I finished ages ago, and didn't get around to shooting until just now.
My favourite move in Warhammer 40k: Space Marine is when you get the Power Axe, if you attack enough times in melee (the right mouse button) then Captain Titus leaps in the air, spins and slashes. There's a trail of electricity behind him from the axe too. It's hard to describe exactly, but I know it's in this video at 6:30 - [link]
*Draws blatant Rainbutt fanservice*