I love, love, love El Mercado on Southport, right next to Tango Sur.
Basically, everything that's on Tango Sur's menu is available for sale at El Mercado over the counter at bargain basement prices. The meat counter in El Mercado is essentially Targo Sur's meat prep kitchen (the two are connected through a doorway in the back).
You can get fillet mignon and rib eye steaks of fantastic quality for $9.99 a pound. They've also got just about every cut of meat imaginable at or below that price point. The only extremely minor inconvenience is that it's sometimes a little hard to figure out what's what since the hand written board listing cuts of meat is in Spanish, with sparse translation. Lately the guy behind the counter speaks English, but every once in a while there's someone who doesn't. In the past, I've gotten around this problem with a form of charades wherein I'll say the name of a cut in Spanish, point the the approximate place on my body I assume it's from, and then wait for the butcher to agree or correct me by either pointing, showing me the actual cut, or a combination of the two. It's actually a lot of fun, and last time it happened everyone seemed to get quite a kick out of it, myself included.
My favorite thing there by far, though, is the sausage. $1.50 a pound for some of the best stuff around. I actually stopped by there yesterday around noon to pick some up and had to come back because the guy behind the counter hadn't made it yet. The sausage is just awesome. It's a beef/pork mix in all natural casing. Aside from just grilling them straight up, I also use them as a base in my tomato sauces to add extra flavor.
I don't think I've bought a steak anywhere else in the past 6 or 8 months since I started going here. I can't recommend it highly enough.
One thing to note, however, is it's cash only. Same as Tango Sur, if I remember correctly.
El Mercado
3767 N Southport Avenue
(between Grace St & Waveland Ave)
(773) 477-5020