Is there a Naruto and One Piece crossover manga? Is there a Naruto or One Piece crossover manga or anime?  Have both of the authors collaborated in anyway?
Kishi and Oda make reference to each others works from time to time. 

For example, One Piece made a reference to Naruto in chapter (766):. 
Nami's dress with has symbol on it, and how there's a fox eating ramen with a whirlpool on its back. 
Kishi also put a One Piece skull and crossbones (along with the straw hat) on the very last page of the last chapter of Naruto. 

Although there are no offical crossovers, there are many fanfics about this.