I am amazed at how many developers are still using windiff or VSS diff tool. Beyond Compare is great tool that I use almost daily. It allows you to diff files and folders using the context menu of Windows Explorer as well as through their UI. It is as simple as right clicking on a file choosing “Select to Compare”, right clicking another file choosing “Compare XYZ.doc”. For $30 it is a great buy and real time saver.
You can download a free trial at their website http://www.scootersoftware.com/