I've been searching for good tips regarding this matter and I haven't seen anyone mentioning anything about new Cain's legendary set: "Cain's Fate". I know this is kinda common sense but I figured that some people might've missed this.
So the thing is that with the new patch 1.0.4 they introduced new lineup of earlier sets and Cain's Fate yields 30% more experience when 3 pieces of set is worn. One thing to note is that when you're buying these items off auction house you MUST search for non-legacy pieces because older version doesn't give this bonus.