Ubuntu is growing so well (so fast) and now it's become most popular Linux distro ever, although initially it's debian based linux distro eventually ubuntu become more popular than debian it self. Ubuntu give convenience developer/user to remastering or rebuild it's system (desktop) in order to make better or find other shape of linux distro. Here are list of Linux distros based on Ubuntu sorted by  Top 100 distrowatch most popular distro list

Linux Mint
Linux Mint is an Ubuntu-based distribution whose goal is to provide a more complete out-of-the-box experience by including browser plugins, media codecs, support for DVD playback, Java and other components.
Lunux Mint Official website : http://linuxmint.com/

Lubuntu is a fast, lightweight and energy-saving variant of Ubuntu using the LXDE (Lightweight X11 Desktop Environment) desktop. It is intended to have low-resource system requirements and is designed primarily for netbooks, mobile devices and older PCs.
Lubuntu Official Website : http://lubuntu.net/

Kubuntu is a free, user-friendly Linux distribution based on KDE's desktop software and on the award-winning Ubuntu operating system. It has a biannual release cycle and at least 18 months of free security updates for each release.
Kubuntu Official Website : http://kubuntu.org/

Ubuntu Studio
Ubuntu Studio is a variant of Ubuntu aimed at the GNU/Linux audio, video and graphic enthusiast as well as professional. The distribution provides a collection of open-source applications available for multimedia creation.
Ubuntu Studio Official website : http://ubuntustudio.org/

Bodhi Linux
Bodhi Linux is an Ubuntu-based distribution for the desktop featuring the elegant and lightweight Enlightenment window manager. The project, which integrates and pre-configures the very latest builds of Enlightenment directly from the project's development repository, offers modularity, high level of customisation, and choice of themes.
Bodhi Linux Official Website : http://bodhilinux.com/

Zorin OS
Zorin OS is an Ubuntu-based Linux distribution designed especially for newcomers to Linux. It has a Windows-like graphical user interface and many programs similar to those found in Windows.
Zorin OS Official Website : http://zorin-os.webs.com/

Joli OS
Joli OS is an Ubuntu-based Linux distribution. It is geared towards extreme user-friendliness so that any computer user can install it with just one click. Besides the standard ISO image, the distribution is also provided as a Windows executable file which can resize an existing Windows partition and install Joli OS as an alternative operating system.
Joli OS Official Website : http://www.jolicloud.com/

Mythbuntu is an Ubuntu-based distribution and live CD focused upon setting up a standalone MythTV system similar to KnoppMyth or Mythdora. It can be used to install a standalone frontend, backend, or combination machines. Mythbuntu uses Xfce as its default desktop and provides a graphical Control Centre to configure the system.
Mythbuntu Official Website : http://www.mythbuntu.org/

moonOS is a complete, Ubuntu-based distribution featuring the LXDE and Enlightenment 17 desktop managers and imaginative, original artwork.
MoonOS Official Website : http://www.moonos.org/


Netrunner is an Ubuntu-based distribution with a focus on desktop computing. It boasts a carefully tuned KDE 4 desktop with many integrated GNOME applications to offer users a selected mix of popular and powerful applications.
Netrunner Official Website: http://www.netrunner-os.com/

Vinux is Ubuntu-based distribution for designed for visually impaired users.

Vinux Official website : http://vinuxproject.org/

BlankOn is an Ubuntu-based distribution developed by the Indonesian Linux Mover Foundation and BlankOn developer team. It is an Indonesian distribution that includes a variety of software that is widely used by consumers in general and also will be available in various local language. In indonesia Blankon was very popular distro beside of Ubuntu.
Blankon Official website : http://blankonlinux.or.id/