I came across this article on IGN that mentions some of the riders in the game:
 
IGN: MX vs. ATV Reflex features Ricky Carmichael, Jeremy McGrath, and more
 
That's a stellar lineup so far. I can't wait to find out who else is in it!

I GOTTA FIND BUBBA!!!

Hahaha, nice to know that no one got the joke. ;) 
 Anyway, the list, while it does feature a few of the top guys, which is good to know, there's still so many they haven't announced yet. Having Jeremy McGrath and Ricky Carmichael in the game is a big deal, though. I hope James Stewart also makes it into the game.

James Stewart was the first name announced. It's even in the link I posted. lol I'm hoping Chad Reed is in it.

Looks like they added another name in Kurt McCabe. They put up an interview with him here:
Featured Rider: Kurt McCabe
 
I'm not familiar with him but that's a good thing they're giving lesser known guys a chance to shine. Everyone knows Bubba and McGrath and Carmichael, etc. But there's a ton of other dudes that work hard like McCabe who don't get as much notice.