If you only need to strip the tags, you could use LINQ to XML...
XDocument doc = XDocument.Parse(html);
doc.Elements("script").Remove();
Don't forget about other attributes that can execute javascript....
doc.Attributes("onclick").Remove();
...something like that.
There are a lot of different ways for javascript to be executed though so it's tough to be completely thorough. I'm sure there are more robust solutions out there.
http://blog.sonerdy.com