Emacs

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

Keyboard Macros:

'C-x (' to begin recording
'C-x )' to end recording
'C-x e' to execute the macro (eg. 'C-u 50 C-x e' to execute the macro 50 times

Example : incremental searching (plain or regexp) within a macro to find the next place you need to munge and then use a combination of cursor positioning, killing, yanking, copying to registers and whatnot to munge the text however necessary. Then you just 'C-x e' to your heart's content.

Fill Mode:

`ESC-x auto-fill-mode` sets autofill mode
`C-x set-fill-prefix` set the fill prefix (enter in whatever on earth you want to be the prefix for your lines)
`ESC-q` will re-"soft newline" the current paragraph, inserting the fill character as prefix.

Example: In the c(++) modes when editing multi-line comments started with /* (i.e. just type the comment as all one paragraph, then ESC-q will re-format, leading each line with the right number of tabs and a '*' ).

All above courtesy of Bill Baxter and Scott Larsen

XEmacs Toolbar/MenuBar Toggle (Scott Larsen, Max Smolens)

(set-specifier menubar-visible-p (not (specifier-instance menubar-visible-p)))
(set-specifier default-toolbar-visible-p (not (specifier-instance default-toolbar-visible-p)))
M-x tool-bar-mode