tl;dr: a broken timing belt always means some sort of damage.
Like Brian says, interference engines are obviously at risk of the most straightforward damage: pistons hitting valves with great energy, causing ma$$ive destruction.
Here is a cautionary video illustrating some of the parts that can be immediately broken, causing a appalling domino effect of damage.
Even if the pistons and valves can't technically occupy the same space, a broken timing belt is effectively a high energy whip slashing around in your engine bay. The easiest way to eyeball what could be damaged by a broken belt is to look at all the components that are dependent on, connected to or adjacent to the belt. Assume that they'll all be hurt and that, in their death throes, they will lash out at other blameless parts purely out of spite.