The C&C Guild is one of the oldest Command & Conquer modding communities still on the web. Formed in 2002, it has gone through quite a few changes, merging with Origin Network in 2004 to form Revora Creative Community.
The Guild offers free hosting to mods and resources for all of the C&C games, giving perks such as unlimited webspace and bandwidth (within reason, of course), as well as your own forums. More on that can be found at Revora's Hosting Portal
Many popular mods are currently hosted at the Guild, such as Speeder's Mental Omega. Additionally, the Guild boasts one of the largest community resource sites around - YR Argentina, which is currently undergoing improvement. Also, a wealth of tutorials are located on the Guild's main site itself to assist with most modding troubles. And for those that aren't there, the forum members will be glad to assist.