Debug Visualizers don't work for arrays.
You can write a custom visualizer for an object of any managed class except for Object or Array. http://msdn.microsoft.com/en-us/library/e2zc529c.aspx
The visualized type has to be attributed [Serializable] or implement ISerializable. Arrays don't implement ISerializable and cannot be attributed. For some reason.
Lists work, though, so I sometimes make a new list<>, just for debugging purposes.