If you're a Safari user you should check out PimpMySafari.com, a website that catalogs some of the better plugins for the browser. While the idea for the name came from the MTV series on blinging car customization called "Pimp my Ride," PimpMySafari is a bit more practical and useful.
Safari doesn’t have an official ‘extension architecture,' so many users don’t know about the extensions offered on the site. The emphasis is on plugins that work within Safari, but occasionally the creators have included apps they feel are essential - and for the most part, they are on track. There's no rating system, but only the better apps are included in the first place.
PimpMySafari's three essential extensions are: Saft, PithHelmet and Stand.