Regardless of your particular browser preference, there's no denying that Safari has some great built-in functionality vis-a-vis the core OS X apps. I've always wanted to like Safari, but I never really have. Instead, my browser of choice has always been Camino, with an occasional Firefox window now & then.
In an effort to increase Safari's usability for me, here are a few plugins I've recently adopted.
SEARCH FROM THE SAFARI ADDRESS BAR: This has always been a great feature that Safari has lacked. Now you can add the functionality to Safari with Keywurl.
REMEMBER PASSWORDS ON SECURE WEBSITES: Let's face it, the Mac Keychain is fairly secure, yet Safari insists on honoring the "autocomplete: off" key for most banking websites. Fear not. This Autocomplete Always On script patches WebKit to ignore the "autocomplete" flag. While you will probably have to repatch Safari following major updates, this gets the job done quick and easy.
VIEW SITES AND PHOTOS IN TRUE FULL SCREEN: There's expanding the browser window, and then there's EXPANDING the browser window. PicLens does true fullscreen right. It's the ultimate Flickr browser.
ADD EXPOSE TO TABS: I love Exposé. I love tabs. I love TabExposé.
ADD GREASEMONKEY FUNCTIONALITY TO SAFARI: Yes, all the "cool kids" love the Firefox. Why? GreaseMonkey (mostly). Now you can add GreaseMonkey functionality to Safari.