Not sure I'd call them a "sleeper" but as far as 100% merino wool clothing goes I'm a big fan of Minus33. Not as expensive as most of the hunting brands but also not as cheap as some of the others mentioned. It's been a lot more durable and comfortable than the Icebreaker and Black Ovis merino wool I've used.
For most applications I've come to prefer a merino/nylon blend like First Lite's Aerowool or some of the Voormi stuff but for straight merino I like Minus33 best of the ones I've tried.
I think what I will do is wait for sales of a number of the brands that have been mentioned here and jump on them then. I did go to the LL Bean website and they do have a sale going on. It seems like very often you find that a company has sold out of the most popular sizes.
Filson makes great merino stuff. You can get 10% off my signing up for their email, or go to mc reynolds out of devner and get 15% off with email sign up. I have the tops and bottoms in 280gr, and the 400gr half zip. Very soft and warm.