Zier's in Wilmette is hands down my favorite butcher. It's on Ridge just off of Lake Ave (and maybe 4 blocks or so west of Green Bay Rd). I live in the northern suburbs now, but I would drive up there just to go to Zier's when I lived in Chicago. As a bonus, The Backyard Barbecue store is in downtown Wilmette... About two minutes from Zier's.
Every kind of beef is cut to order right in front of you. There's nothing quite like seeing them take a big honking strip loin and cut off the exact size that you want. THAT'S what I look for in a butcher. You can also order special cuts that he can get within a few days.
The service is impeccable. One time I bought a chuck roast to try a new chili recipe. Dave Zier asked me what I was making. I said chili, but that I wasn't looking forward to cutting the three pounds of meat into a 1/2" dice. He said, "Oh, let me do that for you." within like 3 minutes, I had 3 pounds of chuck cut into a PERFECT 1/2" dice. Unbelievable! They will also trim anything down for you if you just ask.
It's all prime. The New York strip steak tastes like butter every single time. He even has Kobe beef if you want to try.
They also smoke quite a bit of their own meat to sell. I've been there many times when they've had something smoking and the smell is heavenly.