Capcom showed a new version of Street Fighter X Tekken at Captivate in Miami last week (media embargo lifted today). They also released a number of new gameplay trailers including the one below that features a fight between some of the most recognised characters in both series, Ryu and Ken on the Street Fighter side and Kazuya and Nina on the Tekken side.
If you want to learn more about the game you should check out our impressions of the game found in this preview.