Marius - www.mariusnet.com
Since the downfall of the PlayMyth server, Marius has been the home of online Myth gaming. Not only is Marius a server for the Myth series, it also accomodates Marathon junkies (another great series of games by Bungie) for their online play. You will also find areas for map downloads, forums to talk with other players, and more.

Project Magma - www.projectmagma.net
Makers of the amazing Mazzarin's Demise series and other projects (including work on updates for Myth 1 & 2), the Magma fellas are another big reason for Myth's continued popularity. Their forums are also home to many map-makers and Myth enthusiasts alike.

Mything.org - www.mything.org
A well-kept Myth site that provides players with just about everything: news, 3rd party map information, community history, and much more. Definetely a site worth checking out.

The Tain - tain.totalcodex.net
This nice well-built site is a massive file archive for the Myth series. You will find everything, with nice information tidbits, from maps to map-making resources. A must-bookmark for any myther!

Myth Vault - gallery.totalcodex.org
Big gallery of user-submitted screenshots, videos, art and more.

Bungie - www.bungie.net
They started this whole I've-given-up-a-personal-life-to-play-until-4AM thing. I suppose that's worth a link.

myth.bungie.org - myth.bungie.org
Although it's not as updated with news anymore, MBO still has loads of information on Myth. Good place to do research if you're new to the game.