AskUbuntu
A popular question and answer site for Ubuntu users and developers

Ubuntu Forums
Forums with an exhaustive list of subject areas, including user support for Ubuntu and its flavors

Mailing list
The ubuntu-users mailing list is designed for technical support from and to the community

IRC channels
The Ubuntu IRC channels #ubuntu and #ubuntu+1 give user support for the released and development versions, respectively

Ubuntu Manual
A comprehensive beginners guide for the Ubuntu operating system

Useful Links
A list of useful links to guides and more not directly maintained by the Ubuntu community

Edubuntu
Edubuntu website
Edubuntu documentation

Ubuntu GNOME
Ubuntu GNOME website
Ubuntu GNOME documentation

Kubuntu
Kubuntu website
Kubuntu Help and Support

Ubuntu Kylin
Ubuntu Kylin website

Lubuntu
Lubuntu website
Lubuntu documentation

Mythbuntu
Mythbuntu website
Mythbuntu Help

Ubuntu Studio
Ubuntu Studio website
Ubuntu Studio documentation
Ubuntu Studio Community and Support

Xubuntu
Xubuntu website
Xubuntu documentation
Xubuntu Help & Support

Ubuntu Community
Read more about the community, its structure and ways to start contributing

Ubuntu Fridge
The official information hub on the Ubuntu community

Ubuntu wiki
The Ubuntu wiki is one of the central repositories for development assets