There might be some more Encuentros of that sort, but I only include events that I can recommend personally, because I have been there or because I know the organizers and participants well enough to guarantee for their "esprit milonguero".
So, these are the events that me and/or my friends visit in 2012:
Pasionara Milonguera, Côte D'Azur, France, January 27-29
Mirame, Montpellier, France, February 24-26
Rendez-vous Milonguero, Bologna, Italy, March 2-4
Montecatini Terme Tango Festivalito, Montecatini, Italy, March 30 - April 1 (read review)
Abrazos - Encuentro Milonguero UK, Devon, United Kingdom, May 4-6 (read review)
Les Cigales, Carpentras, France, May 17-20 (read review by Ms. Hedgehog)
Tango del Mar - Encuentro de Abrazos, Constanta, Rumania, June 8-10 (read review)
Raduno Rural, Slovenia, Juni 29 - July 1 (read review by Ms. Hedhehog)
Encuentro Milonguero, Kehl, Germany, September 13-16
Festivalito Rural, Celje, Slovenia, September 7-9 (read review)
Ensueños, Valongo, Portugal, October 4-7 (Facebook event)
Ensueños, Valongo, Portugal, October 4-7 (Facebook event)
FCA (Tangokombinat, private party)
Raduno Milonguero, Impruneta, Italy, November 1-4
Looking forward to meeting you there!