My top three polishes were;
Avon - Sapphired Up is a straight up blue polish, great for nautical themed nail art.
Danglefoot Polish - Magneto, is a magnetic navy polish with holographic particles. When you use the magnet on it the polish changes to a lighter blue shade. This is great for easy galaxy themed nails.
And the winner is Danglefoot Polish - Oh Plesiosaur, which isn't a blue however it ended up in this pile because it is a Danglefoot. I like this one because it is a very holographic dark grey, charcoal polish.