I got married at the Registro Civil in Belgrano (on Cabildo) last week. My husband is Argie, I'm American. We made the appointment a month in advance and I had to come in for a Spanish "test" to see if I needed a translator or not. The lady asked me these questions (in Spanish): "why did you come there today?", "what are you doing in BsAs"?, "how long have you been here?", then some simple questions as she was filling out our paperwork, such as age, but otherwise she just used my passport for other info. I passed this test!
We were given a list of hospitals we could go to to get a blood test, so we went for the blood test exactly one week before our wedding, and picked up the results a couple of days before the wedding. Actually, three days before the wedding we needed to bring the DNIs of our two witnesses, along with my passport and my husband's DNI. Since we didn't have the blood results back yet (since Monday was a holiday), we took a paper as proof that we had gone in for the blood test and were awaiting the results, then the day before the wedding we took the blood results to the Registro Civil.
The blood test and results were a joke. I can't remember the exact prices, but I think the actual blood test was around $70 pesos, then when we went to get the results, we had to pay for a consultation, something around $120 pesos. The consultation was 1 minute long as the doctor told us we were negative for syphilis and that was it.
So all in all, as a foreigner, I just needed my passport with a valid tourist stamp (which they did check).
The ceremony was fast! We were the last scheduled ceremony of the day, so it started an hour late, but went quickly. The judge asked where we met, then proceeded with saying a few words, we stood up, exchanged rings, kissed, signed a registry book, then the judge left and we stayed in the room and took a few pictures. Remember to bring your passport and your spouse's DNI to the ceremony, along with your witness's DNIs.