Visual Studio comes with two commands for navigating among the various things in the task list: View.NextTask and View.PreviousTask.
This blog post has moved to http://saraford.net/2008/03/25/did-you-know-you-can-create-keyboard-shortcuts-to-navigate-among-the-various-task-list-categories-view-nexttask-and-view-previoustask-179/