Sweet!
I would recommend Colvin Run (Milonga Color) on Friday night, Chevy Chase Ballroom on Saturday (Milonga Portenia), and Freedom Plaza (Milonga a la Libertad) on Sunday night if the weather is good. All venues play traditional music, almost exclusively. I don't know of any nuevo/alternative venues offhand.
I have never been to Colvin Run, but I'm pretty sure it's regarded well. The dj for that night, Yulia, is fantastic. She's got great music and is very good at reading the crowd and keeping the energy level going. I don't know what the dress code is.
CCB is the milonga I frequent most. It's a bit of a dive, but it tends to be pretty well attended; there's something about that venue that just always seems to work. It's got a wonderful soft, fast floor, too. I don't know that dj offhand, so I can't comment on that. CCB tends to be a bit dressy, but they won't throw you out if you're casual (and I should know).
If the weather is good and you can stay in town for Sunday evening, definitely go to the milonga at Freedom Plaza. The venue is gorgeous, and it's just a great atmosphere. Don't wear your best shoes--it's outdoors and you're dancing on granite. There are words carved into the stone, so you've got to be careful to keep your heels out of the grooves (they're perfectly sized for womens' heels), and there are also these little metal thingies that stick up from the stones just enough to catch the edge of your feet. It sounds bad, but after a tanda you learn to deal with them and forget about them. Dress code is the most casual of any of these. The music on that night (9/13) is done by Jake Spatz, who is not my favorite DJ. He tends to play very old, very rhythmic music almost exclusively and IMO is not the best at managing a group's energy. But the experience of dancing outside (
http://www.tangobarrio.com/dance.html) is well worth it. Bring a bottle or two of water, and use the bathroom before you go!
I'd be more than happy to meet up and say hi. PM me if you're interested.