My current mog. It might be my favorite one yet. It even manages to to have every single piece from a completely different set (I usually try to limit myself to no more than 2 pieces from any one set.)
Sources:
Helm: Pre-MoP Theramore scenario loot
Shoulders: Heroic Firelands
Back: Level 50 BoE green
Chest: T14 LFR Tier
Belt: MoP PVP Belt
Hands: Wrath PVP Gloves
Legs: MoP questing green
Feet: MoP Heroic dungeon drop
Main Hand: Nefarian (Vanilla version) drop
Off-Hand: Cataclysm crafted 346 blue
Tabard: Sunreavers Tabard