"Ever wanted to rid the web of the scourge that is Adobe Flash, but still retain the ability to view Flash whenever you want?" When it comes to sales pitches, that one is pretty difficult to beat.
Ever since Flash was unleashed on the web, it has been used for obnoxious and annoying ads. About the only web technology which has been more frequently abused is the animated GIF. For as long as I can remember I have disabled Flash, or plugins entirely, to avoid the annoyance. Firefox users have had extensions which manage flash, but Safari/Webkit users have been left out in the cold.
Several months ago someone created a now-defunct project on Google code simply called "clicktoflash". The premise was simple: replace all instances of Flash with a subtle grey box, and if you want to load it, click it (hence the name). The project was abandoned and deleted nearly as quickly as it appeared, but fortunately it had already been "forked" by Jonathan 'Wolf' Rentzsch who now maintains clicktoflash at github (which reminds me, TUAW is now on Github too).
Newer versions include the ability to "white list" a domain (meaning that Flash will always load for pages from certain sites) or load every Flash object on a page, rather than having to click all of them separately. It will also alert you of new versions and lead you through the installation process in a matter of clicks.
If you visit YouTube you will also find that if you control-click on movies, you are given a chance to load either the Flash OR H.264 versions of movies, or open the movie in QuickTime Player, or download the H.264 version. That alone makes it a great addition to any Mac. Be sure to checkout the settings under the Safari > ClickToFlash menu for additional controls.
I first learned about ClickToFlash from John Gruber who noted ClickToFlash is "a legitimate browser plugin that goes in ~/Library/Internet Plug-Ins/, not a dirty input manager hack. I can't remember the last time a piece of software made me this happy." I have to agree. ClickToFlash is a perfect example of "addition by subtraction" proving that you can make something better by taking something else away.
ClickToFlash is a free download and supports Tiger, Leopard, and Snow Leopard. It requires Safari 3 or higher.