XPath Builder

I am looking for a good Friday evening project and was thinking about an XPath Builder tool. It seems to me that the biggest problem in getting Xslt files to work is getting the XPaths right.

I was thinking about a tool where you could type in an XPath, set a Context Node and evaluate it. The result (the found items) should be shown in a grid below much like the SQL Server Query Analyzer.

Such a tool would plug nicely into the new Sitecore IDE which we are building at the moment.