This answer implies that there is no character statistic or class that helps blocking. Is there a passive? This answer lists some of the items that have the +% Chance to Block affix. What are the best-in-slot items with +% Chance to Block?
This is relevant because the achievement An Impenetrable Defense requires a Barbarian to block five attacks in a row. The higher your block chance, the easier it is to get the achievement (I recommend an Iskatu run on Normal for that achievement). What is the maximum Block chance?