Great website with snippets of all the best music for DJing. It has lists of traditional tango songs for social dancing grouped by orchestra/singer/period with sound previews for every song (beginning and middle of each song).
Tanda of the Week
This blog is updated weekly with a new tanda. The site also has great information and advice about DJing.
Keith Elshaw has spent the last 10 years restoring old tango recordings.
Great site with tons of information including lots of discographies.
Great website with lots of history articles about the music, dance and poetry of tango.
Classic Tangos Arranged by Orchestra
Guide to Post Golden Age Recordings
Veronika Fischer's Website
This website has a great guide to tango djing and lists of non-tango songs good for dancing.