Using the Keyboard to Navigate the Material/Map List

You can use a few keyboard shortcuts to navigate the Material/Map List.

Up Arrow and Down Arrow Keys
Up-arrow and down-arrow move through the list, one entry at a time.
Left Arrow and Right Arrow Keys
When you are at an entry that is a group header, left-arrow collapses the group if the group is open, and right-arrow expands the group if it is closed.
Enter Key
When you are at a material or map entry, Enter adds an instance of the material or map to the active View, and centers the new node in the View.

When you are at a group header entry, Enter collapses the group if it is open, or expands the group if it is closed.

These shortcuts (aside from collapsing/expanding groups) also work in the Browser's list of search results.