Here is a list of websites that I have found to be useful in keeping up with Supreme Commander news, strategies, and ideas.

GPGnet Official Forum:

Supreme Commander Live:

GameReplays [Supreme Commander]:

Supreme Commander Units Database:

Recommended Strategy Guides

If you are new to Supreme Commander multi-player, I recommend taking a look at the following guides courtesy of AngryZealot and Gnug215.

AngryZealot's STFU Guide to Stop Sucking at SupCom
Gnug215's Beginner's Guide to SupCom
Gnug215's Comprehensive Guide to SupCom

I especially like Gnug's Comprehensive Guide and I staunchly recommend it to new players.  All the material in that guide is pure gold, and it will make a world of a difference.  After participating in Gnug215's mentor program, I decided to create my own Supreme Commander unit guide, which is found here on my website.  Each unit has a detailed description along with common practical uses I've personally seen in multiplayer games.  I wanted to avoid making a strategy guide since I believe it's up to the player to develop those techniques.  Knowing good strategies is not the same as having the ability to put it into practice.  That kind of gameplay comes with lots of experience, which can only be accomplished by playing the game.  So what are you waiting for?  Get out there and play!