These hotkeys work only in "viewport" windows (the four main editor windows where you view the world)

Alt-1 Wireframe
Alt-2 Zone/Portal
Alt-3 Texture Use
Alt-4 BSP Cuts
Alt-5 Dynamic Light
Alt-6 Textured
Alt-7 Top
Alt-8 Front
Alt-9 Side
Alt-0 Lighting Only
Shift-A Actor: Select All
Shift-B Surface: Select matching brush
Shift-C Surface: Select adjacent coplanars
Shift-D Actor: Duplicate
Shift-F Surface: Select adjacent floors
Shift-G Surface: Select matching groups
Shift-I Surface: Select matching items
Shift-J Surface: Select all adjacents
Shift-M Surface: Save selected surfaces
Shift-N Clear selection
Shift-O Surface: Intersect with saved selection
Shift-Q Surface: Invert selection
Shift-R Surface: Load saved selection
Shift-T Surface: Select matching textures
Shift-U Surface: Union with saved selection
Shift-W Surface: Select adjacent walls
Shift-Y Surface: Select adjacent slants
Shift-Z Surface: XOR with saved selection
Ctrl-C Copy
Ctrl-V Paste
Ctrl-W Actor: Duplicate
Ctrl-X Cut
Ctrl-Z Undo
Ctrl-Y Redo
Ctrl-A Brush: Add
Ctrl-S Brush: Subtract
Ctrl-I Brush: From intersection
Ctrl-D Brush: From deintersection
Ctrl-L Save
Ctrl-E Save As
Ctrl-O Load
Ctrl-P Play Map

W/A/S/D Move Viewpoint
P Preview
B Toggle Brushes
H Toggle Actors
I Toggle Actor Info
G Toggle Selection Highlight
T Toggle Terrain
F Toggle Distance Fog
O Toggle Volumes
Q Toggle BSP
R Toggle Static Meshes
Z Align cameras to selected Actor
Left Square Bracket Terrain: Shrink Tool Radius
Right Square Bracket Terrain: Grow Tool Radius
Minus Reduce grid size
Equals Increase grid size
Spacebar Maximize/restore current viewport