According to the highly dubious and open to anyone to edit Wikipedia, Vinnie Jones, who plays Juggernaut in X-Men: The Last Stand, has been quoted as stating that his contract extends into the next two movies.

However, the quote from the Vinnie Jones Wikipedia entry through Digg says:

In 2006, Jones plays Juggernaut in X-Men 3. In an interview since filming wrapped he has stated that he is signed for more movies: "I've signed for X-Men 3, 4 and 5...that's my contract...yes." There is also a possibility that he may revive his Juggernaut role in the X-Men spin-off film Wolverine...

Yet there is no source link or statement. Well I'm 100% dubious of that one, considering the news we had on the messed up IMDB entry for Spider-Man, which is now corrected and identified as a demonstration of the sites possible innacurracies, then there's no surprise that a totally reader editable site could have an innaccurate quote in it.