Since there's already a thread with Pokemon, what if the OP characters were to be duelists of Yu-Gi-Oh. (One Piece/Yu-Gi-Oh crossover) I've been thinking about this for a while and came up with matches myself.
Zoro - Flame Swordsman, Masaki the Legandary Swordsman
Sanji - Bistro Butcher, Just Desserts
Ace - Red Eyes Black Dragon, Twin-Headed Fire Dragon
Chopper - Kuriboh
Robin - Harpie Lady, Harpy Lady Sisters, Elegant Egotist