Saw this on Scott Hanselman's blog (link to post) but the guys at Binary Fortress make a great little tools called ASP.NET ViewState Helper. It allows you to see the site of the ViewState for each page, and also decode the ViewState. Since 98% of what we do at WDG is web based, and the vast majority of that is ASP.NET, its a tool I'll be adding to our suite :)
Download it here!