In case you haven't heard, Safari 5 introduced third-party extensions. This allows developers to write plugins that modify the way the browser behaves or adds browser functionality. Safari Extensions has compiled a list of extensions available for Safari until Apple launches its official Extension Store, but that's a lot of extensions to rummage through. Here's my list of extensions that I use every day.

Adblock - This is by far the most necessary extension for me. It blocks ads. Dead simple. My only complaint is the ugly button it installs into your toolbar. That's easily dropped by "customizing toolbar."

HelvetiReader - Restyles your Google Reader feed into something much more aesthetically pleasing.

NoMoreiTunes - Stops Safari from auto-launching iTunes when browsing the App Store or iTunes Music Store in the browser.

Autocomplete - Overrides sites' request to block autofilling field information, i.e. passwords.

Google Lightboxer - Nice lightbox for Google Image searches.

Facebook Zen - Allows you to block various Facebook "features" such as ads, suggestions, etc.

CloudPreview - You may remember my review on Cloud.app. This extension previews HTML5 video from Cloud.app in the browser without having to download the file first.

WideYouTube - Defaults YouTube videos to the larger, wider format.

Enjoy, and feel free to add your own.