indent-rigidly (start end arg)
Indent all lines starting in the region sideways by ARG columns.
Called from a program, takes three arguments, START, END and ARG.
You can remove all indentation from a region by giving a large negative ARG.
The real pleasant surprise is that it works with negative arguments just the way you expect, like C-u - 3 M-x indent-rigidly moves a chunk of text 3 columns to the left. I mean, I wouldn't have been surprised if I read the documentation first before fiddling with it, but I didn't, so I was.