Brandon sent us a great tip that I should have known was in Safari, but that I hadn't found yet. For you paranoids out there, the Safari 3 beta offers an easy way to clean up every single thing you've ever done, including the history, passwords, cookies, and even favicons and Autofill text. Under the Edit menu, there's a "Reset Safari" option which reveals a checklist that lets you hit the reset button on your browser. Firefox users like myself will notice that this was "gently lifted" from the Clear Private Data function under FF's Tools menu.
And it's not just for paranoid browsers out there-- the blogging engine here at TUAW, Blogsmith, is a great program but sometimes hiccups when the cache gets overwritten or pushed out of sync. When it does, the Reset options let me flush the cache in just a few clicks without losing any of my browser windows. If you ever run across a browser-based application that's not doing what you want, this is definitely an alternative to try before actually restarting the browser.