Treasury of Lives
The Treasury of Lives web site is an ever-growing resource of biographies of Tibetan teachers. And not just that, it has collections for traditions, as well as maps and images as starting point for more in-depth research.
For example, if you open the Lodro Gyeltsen entry, You get the various names given, dates of birth and death, tradition, which were his teachers (with their own links), a map of the key geographical areas where he was active, and then a biography which has references to other teachers, monasteries, positions, texts written and much more.
Furthermore the biography then has links to the teachers mentioned, monasteries, famous students as well as other links. This makes it possible in this age of Internet linking to do research that covers much more compared with just reading རྣམ་ཐར་ rnam thar texts and figuring out all the connections. For example, if you select a monastery entry you get both the location, name variants, description and a timeline of famous teachers that were involved with this monastery. As new entries are added in each month, this cross-linking makes the site more rich in future for finding connections.
Something I found fascinating were all the cross-connections between the four Tibetan schools, it was quite common to receive teachings from the various schools and monasteries outside the main tradition. Many other sites are now also cross-linking to Treasury of Lives concerning biographies, such as BDRC and rigpawiki. Check out the map where you could zoom in and find interesting locations based on various parts of Tibet.