Visual Studio 2015 allows you to create links to classes and method in other files from a comment in your C# code:
When the cursor is inside the cref attribute, pressing F12 or selecting Go To Definition opens the corresponding file with the referenced method.
When typing the referenced class or method, IntelliSense autocomplete is available. You can specify an external namespace for the target if needed. The Go To Definition command works with any tag name (e.g. <a>), but for proper XML documentation it is recommended to use <see> or <seealso>.
(This feature was first described by Peter Macej here).