The Vaults of Pandius, Archive of the Mystara Mailing list & Official fan site for Mystara.
The Immortal Project,
including my work on the Lupin pantheon, hosted by the Archmage Solmyr.
Marco Dalmonte Mystaran Page, including the most comprehensive links section for Mystara on the web (far better than mine, at least!).
The Glantrian Personnel Division, a project devoted to the development of the Principalities of Glantri, founded by Markus Montola, and currently ruled by Archduke Kit Navarro.
Paparazzi Glantri, the guild of gossip-dealers of the Principalities of Glantri.
The Empire of Thyatis, home of the Thyatis Character Reference, a project that aims to describe a classical Thyatis.