Comment region in emacs and others

Comment Region :
M-x comment-region, (or in C++ mode, 'C-c C-c')
C-u C-c C-c un-comment
In xemacs, both of these are available when you highlight a region and right click.

Tip: 'C-u' is like "un-next-thing"

Rectangle Ops: (all begin with 'C-x r')
'C-x r d' to delete the current rectangle
'C-x r k' to kill the current rectangle
'C-x r y' to yank it
'C-x r r' which is copy rectangle to register. After you hit 'C-x r r' it asks you for a register to copy the rectangle to. A register is just any letter on the keyboard. To retrieve the contents of a particular register use 'C-x g' then type the key for the register