FlashControl is a Chrome extension which allows you to selectively (or permanently) block Flash content in some or all web pages.
After installation, Flash content is by default blocked, a black square with an "F" where the applet used to be. If you decide you want to access a particular app, then clicking it should reload that content (although sometimes we had to refresh the page as well).
A FlashControl icon in the address bar offers more options. You can click "Allow This Page" to activate all Flash content at your current URL, for instance, or "Block This Page" to turn it off, while "+Whitelist" and "+Blacklist" options allow you to always allow (or block) Flash at particular pages.
But perhaps best of all, if you don't like any of this then you can tweak most of FlashControl's behaviour via its Settings dialog. You can have the extension allow Flash by default, say; enable or disable the omnibox menu; highlight blocked Flash content in various ways, and even block Flash if the computer hasn't been used for a while (perhaps useful in extending battery life).