A complete listing of Tango classes can be found in the "El Tangauta" magazine (Website). Most Tango instructors are independent but there are Tango schools that have a variety of instructors and styles and cater to tourist. I think that by staying with the independent instructors you will learn a more authentic style of Tango. Here is a list of instructors that I used:

Ana Miguel and Oscar Casas: Monday, Wednesday, Friday 13-15 Hrs. El Beso

Mario Bournissen and Rusconi: Thursday 21-22.30 Hrs. Soho Tango

List of Tango Schools

La Escuela del Tango Website

DNI Tango Website

Escuela Argentina de Tango Website