You can use a few keyboard shortcuts to navigate the Material/Map List.
- Up Arrow and Down Arrow Keys
and 
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,
collapses the group if the group is open, and 
expands the group if it is closed. - Enter Key
- When you are at a material or map entry,
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,
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.