The emacs function that seems nifty to me at the moment is string-insert-rectangle. I don't have it bound to any keys, so I invoke it with M-x string-insert-rectangle. Below is its documentation, which can be obtained with M-x describe-function string-insert-rectangle.

string-insert-rectangle is an interactive autoloaded Lisp function in `rect'.
(string-insert-rectangle START END STRING)

Insert STRING on each line of region-rectangle, shifting text right.

When called from a program, the rectangle's corners are START and END.
The left edge of the rectangle specifies the column for insertion.
This command does not delete or overwrite any existing text.

Have fun!