ClickToFlash is a simple app to block the automatic loading of flash content on web pages. It's similar to flashblock for Firefox, but with some additional features like automatically viewing HD videos in youtube. Any flash on a page is simply not loaded, but you can just click on a small icon that ClickToFlash puts in it's place. It works in Safari and on Tiger, Leopard and Snow Leopard. The bonus for me, personally, is that it also seems to work in NetNewsWire, my RSS reader. This vastly reduces the memory usage for the app and makes for a much improved reading experience.
Best of all, it's free.