Milwaukee Mayor Tom Barrett will square off against Governor Scott Walker and you'll be able to stream it here. I'll be live-blogging it, so join me in the comments at 8 Central Time.
Also at that link are links to "Raw Barrett" and "Raw Walker" interviews. Very stark difference in style between the 2 men. It might give you an idea of what they'll be like debating each other. I won't describe the difference myself, but if you watch those 2 videos, I'd love to hear you contrast them in the comments.