@Amit's answer is good because it will work in both Mustache and Handlebars.
As far as Handlebars-only solutions, I've seen a few and I like the each_with_key block helper at https://gist.github.com/1371586 the best.
It allows you to iterate over object literals without having to restructure them first, and
It gives you control over what you call the key variable. With many other solutions you have to be careful about using object keys named 'key', or 'property', etc.