If you want to find anything about tango on the internet, the place to be is Todotango. It has historical articles and biographies of all the major figures in tango history. There is an impressive range of music to listen to and a collection of lyrics and scores. You can consult the best and most exhaustive Lunfardo dictionary. This is proof that the internet makes things possible that were inconceivable in the past. The site is in Spanish and English.
You may already have quite an extensive collection, and want to come up with something that no one else has. In that case we would like to mention the Buenos Aires Tango Club, which is trying to save historical recordings from oblivion by issuing them on CD.
If you are looking for information about Labanotation, the best place to start is the site of the Dance Notation Bureau. It offers a wide range of information and links to other organisations involved with Labanotation.
The standard work on Labanotation is Ann Hutchinson Guest’s Labanotation: The System of Analyzing and Recording Movement, Routledge, London/New York, 2005, 504 p. (ISBN: 0415965624)
An interesting source of books and videos on dance is Dance Books. They have historical books and videos and also works on technical aspects and dance notation. They also publish the Advanced Labanotation series. Their catalogue includes Labanotation scores of a number of historically important choreographic works.