ASPhere

ASPhere is a freeware utility primarily intended for creating and modifying configuration files for ASP.NET.

But they are not only web.config files ASPhere can work with, you can use it for viewing and editing normal XML files and plain text files as well.

ASPhere comes with an editor with syntax highlighting and contextual help, the ability to have several files opened simultaneously and file compare function with highlighting differences. Also, files can be managed in a project.