e.g. Ctrl-o to pop out of insert mode for 1 command only.
or
ctrl-w: delete the last word.
ctrl-u: delete to the beginning of the line.
ctrl-d or ctrl-t: change indent level.
ctrl-h: backspace without leaving the home row.
ctrl-m: without leaving the home row.
There's loads more that are useful in Vim. Of course you've still got the built in Ctrl keys but having ctrl in place of caps is really ergonomic for me.