Improving the widget-title appearance in Twenty Twelve

I’ve created a child theme, so please call off the mods 😉

Feedback I’ve had from a not-for-profit client I’ve been working with is that the Twenty Twelve widget headers don’t stand out as much as they would like.

What steps have you taken to change their appearance?

I don’t want to deviate too far from the base theme to unbalance it so I’m looking for some great examples in the wild.