The first two titles Dead Fantasy and Dead Fantasy 2 were put out quite awhile ago.
I'm surprised the topic hasn't come up here before, so i guess i'll post about it now.
Since some of the newer have been released, thought i'd remind those who may have seen em before.
For those unfamiliar with the series, it pits Square/Square Enix: Final Fantasy characters, vs Team Ninja characters (Dead or Alive and others).
All videos are done by: Monty Oum Monty's site
Dead Fantasy 1:DF1
Dead Fantasy 2:DF2
Dead Fantasy 3:DF3
Dead Fantasy 4:DF4
Dead Fantasy 5:DF5
I linked mostly to Youtube for the videos as they tend to take less time to load. You can watch all 5 (more will be released eventually) at gametrailers.com which is where Monty releases his videos first.