Da oggi è disponibile la versione 14.04 (Trusty Tahr) di Ubuntu e le sue derivate di Canonical:
http://www.ubuntu.com/

Interessante è la Lubuntu 14.04
http://cdimage.ubuntu.com/lubuntu/daily-live/pending/

perché è una LTS di 3 anni
http://lubuntu.net/#Features
"... and, of course, based on Ubuntu 14.04 LTS. "
http://lubuntu.net/#Support
"LTS support (3 years)"

Da notare però, che la Ubuntu 14.04 è una LTS di 5 anni
https://wiki.ubuntu.com/LTS

Alternative:
http://xubuntu.org/getxubuntu/

17.apr.2014

La Xubuntu al momento non ha la versione 14.04, quindi l'unica LTS disponibile è la 12.04:
Latest LTS release: 12.04, Precise Pangolin
The 12.04 release, codenamed Precise Pangolin, is a Long Term Support release and has support for 3 years. To learn more about the release, please refer to the release announcement, which has links to complete release notes as well as highlights of the improvements in the release.

18.apr.2014

Latest LTS release: 14.04, Trusty Tahr
The 14.04 release, codenamed Trusty Tahr, is a Long Term Support release and has support for 3 years. To learn more about the release, please refer to the release announcement, which has links to complete release notes as well as highlights of the improvements in the release.

Vinc.