I just found Plugin Customs, and it's become my new replacement for ClickToFlash. It takes every single plugin, not just Flash, and blocks it until clicked. You have to uninstall ClickToFlash before it works well, but that's a small price to pay.
Update: Plugin Customs 1.2 hates YouTube5, and ClickToFlash has been ported to an extension. I use both ClickToFlash and YouTube5 because YouTube5 is better at using HTML5 on YouTube itself, and I like that ClickToFlash can be set to not automatically load embedded videos. Even so, I can see that ClickToFlash and YouTube5 are the two extensions are most likely to fight.