As far as I know there aren’t any. Plesk bought Helm it’s only major competitor in the Windows space. The only “ok” free panel I know is ISPConfig but it’s only for Linux.
Our company is also searching for an alternative to Plesk, for Windows hosting.
I’m sorry if this is not helpful but why do you wish to have a control panel for Windows? at best its a GUI on a GUI, you can’t touch IIS as it will break the panel etc etc.
To be honest I would stick to a non control panel windows server, its much easier to administrate in my honest opinion.
Question posted in 
2
Answers
As far as I know there aren’t any. Plesk bought Helm it’s only major competitor in the Windows space. The only “ok” free panel I know is ISPConfig but it’s only for Linux.
Our company is also searching for an alternative to Plesk, for Windows hosting.
Edit 25 Oct 2010: DotNetPanel renamed to WebsitePanel appears to be open source:
http://sourceforge.net/projects/websitepanel/
I’m sorry if this is not helpful but why do you wish to have a control panel for Windows? at best its a GUI on a GUI, you can’t touch IIS as it will break the panel etc etc.
To be honest I would stick to a non control panel windows server, its much easier to administrate in my honest opinion.