I wish nunu would get some buffs in order to not be one Skill champion..
My suggestions are
Q-Make it so you get healed for 10% (plus the base healing plus the AP ratio) of the monster HP (Cap 1000) (Only work for big monsters Baron/dragon/mini baron/red lizard/blue golem)
Or
Q-Now deal 50/75/90/110/150 damage to enemy champions and you get healed for the same amount plus you get 15% extra AS from the blood of your enemy (The monsters true damage and heal stay the same this is a second passive of the skill)
Nunu need some love!! And this buffs would not make him broken trust me....i mean he is not even good counter jungler any more with all that elise/kindred/udyr that going on...