If you are spendng a semester in BA you'll definitely have the time to hit all of the must see spots. I agree that Malba, El Ateneo and Teatro Colón are worth checking out. It really depends what you are into -- Buenos Aires is a great walking city and my favorite thing to do is just wander around different neighborhoods checking out cafés, street art, shops, museums, 

-  Feria de Mataderos: Sunday gaucho festival with wonderful regional street food

-  Bosques de Palermo: Walk around the Palermo parks and the Rose Garden

- Check out 'café notables' (historic cafés) like El Banderín, Las Violetas

- Go to a closed door restaurant like I Latina, Cocina Sunae or Adentro Dinner Club

- Drink lots of wine, try Fernet and mate

-  San Telmo Market

- Shops in Palermo Soho near Plaza Serrano

-  Recoleta Cemetery is a must, and if you are into it,  Chacaritacemetery is pretty cool too.

Hey Lyse,

Yes, depends what you're into... I really love the Sunday street art / bike tour with Graffitimundo but that's just me and also did a photography tour with www.foto-ruta.com  - they'll organise a unique tour of a few areas and teach you how to use your camera.

If you're interested in Evita then the Museo Evita on lafinur y las heras is cool - really beautiful building and nice area for lunch outside afterwards.

Have fun! 

Floris Generica is a landmark in Buenes Aires and translates to being a symbol for all of the flowers of the world. As we get more and more global this thought becomes all the more relevant, right? Artist/Architect is Eduardo Catalano.

El Ateneo is an amazing bookstore that opened as a magnificent & flamboyant theater known as Teatro Gran Splendid in 1919. It's now one of the best bookshops in Buenos Aires. Enjoy your "house seat" since some chairs are still the old theater seats.

Palacio Paz Buenos Aires. Great place to get a little Paris in Buenos Aires. Built by an Argentinean diplomat who had spent much time in Paris it is an ode to all things french. Also considered to be one of the most ornate palaces in Buenos Aires.

Teatro Colón - If you're looking for a good cultural hit, you can't go wrong at this opera house. Known for phenomenal & exacting acoustical standards, the first opera here was Aida.

Malba - Terrific nonprofit museum and definitely worth a visit.

Don't know if you like shopping but I love Prüne. This is a great shop for I Must Buy Something Really Great and Leather Now. We'll call it a necessity since traveling breeds the need for great shoes and a bag to carry your uh... camera! Yeah, that's it.

You should totally visit San Telmo on sundays, it's full of foreigners bc they are places to eat from all over the world, people selling all kinds of things, it's a really beautiful place. The Obelisco too, I love the view I have of the 9 de Julio - Avenida Corrientes in the Obelisco, everything is wonderful, it makes me feel a bit like I'm in New York! In that zone, there is the Teatro Colón, which you should totally visit. It's amazing and there are a lot of ballets or operas always playing. You can get the guided tour too. And the Cabildo, but you will eventually see it bc it is in front of the Casa Rosada. Also, Bombonera Stadium for Boca Juniors in La Boca it is a traditional neighborhood and you should visit too, they are always people dancing tango and that stuff. 

That is just a little bit of everything that B.A. has to offer, probably I'm missing a lot of places, but well. Good luck!

You should visit Puerto Madero !!!