Beast, Colossus, Jubilee, and Siren are all reportedly scheduled to appear in X-Men 2 as cameos according to Countingdown.com. With the exception of Siren, there have been previous rumors surrounding appearances by the afforementioned characters in recent months. However, Countingdown.com claims to have a reliable source that says Fox is currently in the process of casting for the the roles of Colossus, Jubilee, and Siren. The site also reports that they have a trusted source that has confirmed Beast's cameo in the upcoming film. Their source also claims that the movie's official site will soon be host to new content.
Hope this is true. I'd like to see Beast even if it is only a cameo.