<p>How would you render a tag cloud within a .NET 2.0+ WinForm application?</p>

<p>One solution that I am thinking of would be using the WebBrowser control and generating to some ad-hoc HTML, but that seems to be a pretty heavy solution.</p>

<p>Am I missing something more simple?</p>

Well, you'll want a control with these major features:
Automatic layout of variable sized string snippets
Automatic mouse hit testing
Those are a bit hard to come by in WF controls.  A RichTextBox with ReadOnly = true gives you the automatic layout, but not the hit testing.  A ListBox with DrawItem can give you variable sized strings and hit testing, but not a natural layout.
I think I would use RTB and make hit testing work with the MouseDown event and GetCharIndexFromPosition(), reading back the tag at the clicked location.  You'll need a bit of logic to find the starting and ending white space around the word.