SPACE - play on/off
Control or Cmd + C/X/V - copy/cut/paste selected region. Paste can be done on another selected track.
DEL or BACKSPACE on a selected region - deletes the region.
S on a selected region - split region in two separate regions.
M on many selected regions - merge the regions.
Double click on the loop handle - turn loop mode on/off.
Shift while dragging region/playhead/loop handle - bypass grid snapping if snapping is on.