Special Joint Anime of Yu-Gi-Oh! Series [Update Sep 18]

According to Dengeki Online, a special movie of Yu-Gi-Oh! will be produced for the 10th anniversary of the series. The movie features the main characters of the three TV series; Mutou Yuugi ("Yu-Gi-Oh! Duel Monsters"), Yuki, Judai ("Yu-Gi-Oh! Duel Monsters GX") and Fudou Yusei ("Yu-Gi-Oh! 5D's"). It will be shown at special events to be held in Japan.

Sources:
Dengeki
Yu Gi Oh! 10th Anniversary official website

Updated on Sep 18th
According to Weekly Shounen Jump, the join anime is a 3D anime movie titled "10th Anniversary Gekijouban Yu Gi Oh! ~Chou Yuugou! Toki wo Koeta Kizuna~". It will be premiered in January 2010.

Source: Scan of WSJ