Blizzard has posted a preview of the levelling rewards in Heart of the Swarm, which includes player portraits, unit skins, and supply building skins. The post also mentions that unit dances will be unlockable with levels as well, which begs the question: "How many dances are in Heart of the Swarm?"
You can check out the full article here.
Source:
Battle.net - Heart of the Swarm Preview: Levelling Rewards
