I've been investigating a few of them.
What I have found so far that seems usable.
Windmill Selenium Watin
Windmill looks like it has the basics (still not sure if I can write C# unit tests with it)
Watin seems awesome with Unit tests..
of the 3, it looks like Selenium is trying to be the most fully featured af the 3 (most recent version is today!)
any comments or suggestions?