I know this show is pretty much old news, but I've recently started watching it on Cartoon Network. As with the new TMNT show, I hated it when it first came out (based on one episode that was heavy on the high-school drama). But the show is pretty darn wild, very true to the spirit of X-Men if not the details. (Most of the characters are in their teens.) And the more I see it, the more the cartoon from a decade ago looks dated and pedestrian.
So far in the few episodes I've seen, I've noticed the following characters:
Sentinel (there's only one so far, and it looks like it could take an army of the comic-book versions)
a British girl with purple hair I suspect may be Psylocke, despite a different first name
Nick Fury (!)
Captain America (!!!)
Airs at 10:30 Mon-Thurs on the Cartoon Network (just after Justice League, which you should be watching anyway). Highly recommended.