Here are some other things I can think of...

- Attend a Futbol (Soccer) match
- watch Polo (during the season)
- wander around San Telmo when the "feria" in on duty
- visit Cafe Tortoni and walk down Av. de Mayo
- walk around Plaza de Mayo and Puerto Madero
- visit the Teatro Colon (guided tour)
- eat lots of dead cow and drink the local Spoof Juice... :D
- visit Recoleta Cementery
- walk around Caminito & historic La Boca
- see the change of the guard by Los Granaderos at Plaza de Mayo
- visit the Rose Gardens and Parks of Palermo

I always enjoyed Feria de Mataderos, and the Campo Argentino de Polo - Hipódromo de Palermo are fun too, and for historical reasons Manzana de las Luces - Iglesia San Ignacio. These are most likely some of the oldest buildings that survive from the early days of the city, late 1500's early 1600's.

More ??

Sam

A few More
 

Here are some good ideas that i could think of...

-- Gauco Party: This gives you the chance to see a real Argentine estancia and see what it was like being a gaucho. Great food, great music, and a lot of fun! Definitely something that not everybody experiences when they come here.

-- Tango Show: I'm not talking about the overly touristy shows or the free ones they put together in the street. If you go to BA, the birthplace of tango, you need to see a real, professional tango shows at an one of the old-school estancias around the city. Also, nothing compliments tango better than a great dinner and a fine glass of malbec wine!

--Tigre: This is where the porteños go on weekends. It's beautiful, with the river and the delta. The boat rides are incredible and romantic, and the crafts fair is authentic and reasonably priced. This is perfect for a breath of fresh air away from the big city, and it is so easy to get to.