Make a Delivery Automator app

I haven't tested this yet, but Make a Delivery sounds like a handy little Automator action that will create a .dmg file from the Finder items you have selected, then attach that .dmg to an email. One quirky thing, however, is that you have to move a resource folder into your Applications directory; it isn't just an action that you can use or turn into a right-click Finder plugin.

In any case, if you prefer an easy way to create .dmg's for emailing (instead of zip archives), Make a Delivery might be just what you need.