argenprop.com and zonaprop.com both good sites. We found ours through these and saw some amazing places.
Saw a great one in maybe not the most ideal neighborhood (Santa Fe y Libertad), but it was sweet:
2 bedroom, 90 m2, private terrace, cable, internet all in U$S 900/mo. Great layout. Kitchen a bit tiny. Came with washer (no dryer, no fridge) Pretty sure came with A/C
It was a nice old style building with green inner courtyard, top floor (6th floor) elevator only went to 5th and you walk the last bit up nice marble steps.
We used a broker who is a friend of our close friend and he is awesome, super nice, speaks english (even had his wife who is a lawyer come with us to sign the documents.) PM me for more info if you are interested.