We've been in South America for a month now and Buenos Aires for half of that time. We've just started to get a feel for the city and all that it has to offer. We have learned a few tips and tricks to make our time in BA a little better. We hope they help you out.
Get a Prepaid Movistar SIM Card
I have an unlocked iPhone 4 and it's been a tremendous help when exploring Buenos Aires. I acquired a pre-paid SIM card from Movistar after we first got here and have been using it on a daily basis. We use Google Maps, Google Translate, and generally just do everything we would normally do using it at home. I tweet, post photos, etc. Do I feel safe using an iPhone here? Absolutely. I'm careful about when/where I take it out but for the most part it's not a concern. We also have a cheap Nokia that we got a sim card for as well. This allows Becky and I the freedom to explore yet always be able to get in touch.
Get a Monedero Card
Bizarrely coins are incredibly hard to come by here. In fact we had to go wait in a bank for 45 minutes to get enough coins to do our laundry the first week we were here. It's better than it was a few years ago but it's still noticeable. Two of the places you'll use coins the most are on the subway and on the busses. Thankfully they've released a pre-paid card system. You can pick up the green cards at any 25 Hours convienience store (it tooks us three stores to find on with cards available). The stores are everywhere. You can recharge your cards at any subway (Subte) stop or any 25 Hours Convieniences. The cards are free.
Upgrade Your Flip Flops and T-shirts
We're staying in the classy Recoleta neighborhood but this seems to be a general theme throughout the city. People dress quite well. You'll probably feel a bit out of place at mid-range restaurants if you're sporting the typical traveler/backpacker uniform of cheap flip flops and an ironic t-shirt. A simple shirt with a collar can spiff you up enough to not stand out. All of that said, the people here are so nice that they will welcome you with open arms and you'll be the only person who noticed you don't have a nice shirt.
Learn Some Spanish
Spanish is a beautiful language, for that reason alone you should learn it. We've found that by making an effort to speak to everyone we meet in their own language it's really been appreciated. This isn't unique to Buenos Aires and is true the world over. Here in Buenos Aires though there is something more than the usual appreciation. There seems to be a genuine pleasure for those we interact with when we whip out our best phrases. Maybe we're just entertaining them :).
Eat Meat
If you're a vegetarian you might want to consider a brief lapse in your eating habits while in Argentina. Simply put the beef is second to none. There are salads, chicken, and ham dishes but for the most part beef is everywhere and eaten all the time. Our favourite thus far has been the Bife de Lomo.
Drink Coffee
There are cafes everwhere and they are used heavily. Everyday around 4-6 they fill up with people having snacks, coffee, and drinks. The coffee has been superb. Tip: Argentinians typically don't drink Cafe con leche past the morning.
Drink Wine
Red is the most prevalent and it's incredibly cheap. A nice wine at a nice restaurant will cost you $10-12 dollars (~40 pesos) for a bottle.
Use the Subte (Subway)
The subway is very reasonably priced (1.10 pesos/trip ~35 cents). It is a relatively clean and fast way to get around some parts of the city quickly. We're luck to have a stop just a few blocks from our apartment.
Buenos Aires Free Tours
This free tour service (they make their money on your tips) is excellent. We've been on two tours so far and have found the guides to be very entertaining, knowlegable, and easy-going. They also make their personal email addresses and phone numbers available to everyone on the tours so you can continue to ask them questions as you explore the city. Well worth the tip you gladly give them at the end of their tours.