Above and beyond the extreme suckage that is Internet Explorer, of course.
 Flashblock. This plugin "blocks ALL Flash content from loading. It then leaves placeholders on the webpage that allow you to click to download and then view the Flash content." Since most of the ads these days use Flash, this is sublime.
 Better Gmail. Bundles a bunch of compiled Greasemonkey scripts to make Gmail clean and efficient.
 Better Gcal. Bundles a bunch of compiled Greasemonkey scripts to make Gcal clean and efficient.
Unfortunately, Firefox epitomizes extreme suckage on OS X, so I haven't found similar functionality for Safari or Camino yet. Stay tuned...