Minecraftforum.net, PlanetMinecraft.com and Feed-the-Beast.com host forums that discuss Minecraft mods. Discussions are available to users under either the Forum or Community section of each of these websites.
Minecraft.net, the official Minecraft website, lists Minecraftforum.net as an official resource on its Community page. Minecraftforum.net's Minecraft modding discussions are available under the Mapping and Modding subheading of the Forum section.
PlanetMinecraft.com hosts a variety of Minecraft-related downloadable content and community discussions. To find the Minecraft modding discussions on PlanetMinecraft.com, click the Community heading, and then select Forums. The Creations section of the forum contains the Modding subheading.
Feed-the-Beast.com provides an assortment of Minecraft mods in the form of a mod pack. Discussions about individual Minecraft mods and mod development are available by clicking the Forum link on the main page and then the Forums tab on the next page. The Feed the Beast section of the forum has a Mods subheading.