In terms of the art, the cover Volume 108 of One Piece features some fun use of color and shading, particularly on Luffy, whose white-dyed pants have an almost holographic look to them.

One Piece Box Set 4 (20 books) -- $100 ($ 186) Currently, there are 104 One Piece volumes that have been translated into English, and you can even grab the majority of them in handy box sets.