Shift+S - Pointer Tool
Ctrl+C - copy objects to clipboard (also ctrl+insert)
[ - grid lower
Ctrl+G - group objects
Ctrl+Shift+C - carve
Enter - create object drawn with block/entity tool
Other Object Operations
Ctrl+B - snap selected objects to grid (based on bounding box)
Ctrl+N - new file
Ctrl+Z - undo
Ctrl+I - flip vertical
Space - While holding the spacebar:
holding the left mouse button allows you to rotate your angle of view
in any direction, while the viewing point remains stationary.
Space+Shift - While holding the spacebar and Shift:
the left mouse button acts the same as above.
z - Pressing the (lowercase) z puts the editor 3D view into its new "noclip" mode (this mode can be disabled in the 3D options dialog)
the mouse acts like +mlook is on (moving it around will change the
player's direction of focus).
Shift+Right-mouse-click - will select an entire brush and bring up
the 3D View context menu, as above.
Ctrl+F - split faces (vertex manipulation) - must have two edges or
Ctrl - hold Ctrl and click to select multiple objects
Shift - create a new camera by holding Shift and dragging with the
left mouse button.
Enter - perform clip
Alt+B - export again