San Salvador, in Belgrano (near Cramer and Sucre), and the Catedral, in the "City", (on 25 de Mayo, nearly opposite the Bolsa) are two Anglican churches with some English services and some English-speaking congregants. If you are American, you may wish to note that the Anglican church in the Cono Sur is very different theologically from the majority of Episcopalian churches in the United States, despite being members of the same communion.
I know that there is an English Mass every Sunday at Mater Amabilis on Arroyo St. and there is an ecumenical protestant service in United Community Church in Acassusso, and they have a bus that leaves from downtown that will take you there... The Buenos Aires Herald usually also has church listings, and i'm sure there are one or two that I am missing.
I hope this can still be a useful link for people because we run an English-speaking christian gathering in Buenos Aires capital in Belgrano. The meeting is an informal service called The Well ("Come all who are thirsty" Isaiah 55) and we meet every other Sunday at the San Andres Presbyterian church at 19.30.
For more info go to facebook.com/thewellbsas and thewellbsas.wordpress.com or send us an email at email@example.com