Extensions make a browser much more powerful and customizable.
I use these extensions for Chrome:
Adblock Plus (Beta)
Ads were yesterday! The successful extension Adblock Plus is now available for Google Chrome.
Firebug Lite for Google Chrome
Firebug Lite for Google Chrome, supported by the Firebug Working Group.
Google Chrome to Phone Extension
Google Chrome to Phone Extension enables you to send links and other information from Chrome to your Android device.
LastPass is a free password manager and form filler. LastPass is also available for Firefox, Internet Explorer and Safari.
New Tab Blank
When you open a new tab, a blank page opens instead of the new tab page.
Adds support to the omnibox to search Python reference documentation.
Reddit Enhancement Suite
Reddit Enhancement Suite - a group of enhancements for browsing Reddit
Mouse Gestures! Quickly and easily navigate webpages using the mouse or keyboard.
Restyle the web with Stylish, a user styles manager. Stylish lets you easily install themes and skins for Google, Facebook, YouTube, Orkut, and many, many other sites.
Find text or links as you type
Xmarks Bookmark Sync
Backup and sync your bookmarks, passwords and open tabs across computers and browsers. Xmarks is also available for Firefox, Safari and IE.
Yet Another Drag and Go
Drag URL to open at Back/Front, Before/After; Drag text to 4 directions to search by using different search-engines.