As for Luffy: doubt he'll get a new gear anytime soon. I think he is just gonna get stronger in a One Piece common way, i.e. training through fights.
Zoro: Hard to tell actually. I think rather than a new "move" he is going to try finding a way to slice through the material the Pacifista are made of.
Usopp: Pepperspray Star, explains itself pretty much by the title. Hit's an enemy and causes them to cry the Rio Grande :P
Robin: Giant clap: Make a giant hand with a part from the lower arm on the ground and give them a good smack.
Nami: Charged mirage tempo; Like the usual one, just charging the immages up, thus incase they are hit, shocking the enemy (hopefully) into coma.
Sanji: I suck at french so I could only think of an english title: shadow leg, kicking in a way that it seems like the opponent is hit twice from the same kick, once by the leg and once by the shadow. (crappy I know. Just can't think of anything else with a kitchen move :P)
Brooke: last waltz, moving at high speed with similar movement to a waltz while the sword gives out the sound to it.
Chopper: Iron point, hardening his hoofs and horns… though I would rather like to see him aquire a way to transform into the other forsm despite the rumble ball.
Franky: No clue. Maybe something like anchors fist, launching a miniature anchor to try to drag down an opponent or similar. Really he has so much stuff allready :P