So I just reached the point in the Thieves Guild questline where I got my own Nightingale armor set. And boy does it look kick ass. My only complaint is the bonus on the hood (15% Illusion spell cost reduction) since I have zero use for it, and the other piece bonuses are amazing compared to it. Here's a pic (not mine):

What about you, found any set that you just keep in your bags to pull out every now and then to make you feel like a badass?