Block Insert and Append

I and A in block mode = insert/append on every selected line.

Keys: Ctrl-V, I, A

After Ctrl-V selecting a column-rectangle, I types text inserted at the start of every line in the block; A appends it. The text is inserted on all lines after Esc.

This is the trick most people don't know exists — and once you know it, you'll use it constantly.

See also: The Three Visual Modes, Swap and Adjust Endpoints