Hextech Protobelt-01, provides health, ability power, and a gap closer with its active.
Sorcerer's Shoes, Best boots for Fizz. Gives speed and magic penetration.
Lich Bane, gives mana, ability power, cooldown reduction, and a passive that synergizes with his W, Seastone Trident.
Zhonya's Hourglass, provides armor, cooldown reduction, and ability power, and an active that makes you invincible for 2.5 seconds.
Void Staff, gives ability power and magic penetration which ignores magic resistance.
Rabadon's Deathcap, gives a LOT of ability power..