If you're looking for keys to remap, these are prime candidates:

  s: synonym for cl
  <cr> (enter): synonym for j
  _: acts like ^ when given without a count, acts like <count>jk^ when given with a count
  <bs> (backspace): synonym for h
  <space>: synonym for l

Doubling up operators with non-motion characters works well, too. For example, operators like 'c' or 'd' probably shouldn't be rebound, and they're often doubled ('cc', 'dd') or accept a motion ('c$', 'd}'), but combining them with another non-motion isn't valid ('dc','cs'). This makes those combinations good candidates for custom bindings. A lot of plugins like surround.vim take advantage of those combinations.

Vimcasts covered this in more depth here: http://vimcasts.org/blog/2014/02/follow-my-leader/