These are the Extensions that I use on every Chromium installation that I have. They are mostly all privacy and security related.
Adblock Plus – My preferred advertisement blocking extension. However, I do whitelist websites that I constantly frequent (such as Reddit).
Block Mixed Content – Blocks insecure active content that may attempt to load from within secure pages.
Disconnect – Tries to stop major third parties and search engines from tracking what you are doing.
FlashBlock – Automatically blocks Flash content.
gleeBox – Allows you to navigate through websites and the browser itself via keyboard commands.
KB SSL Enforcer – Automatically redirects you to the secure version of the websites you are visiting (if they exist).
NOREF – Suppresses referrer information on hyperlinks so no one can see what website you came from.
Perspectives – Helps protect against "man-in-the-middle" attacks by checking to see if the certificate a secure web server is sending you is correct. It also looks at what certificates the website has used in the past.
Reddit Enhancement Suite – The absolute must-have extension if you are a Redditor. As the name implies, it adds a number of enhancements that makes your stay even more enjoyable.
Vanilla – A whitelist manager for cookies. It can automatically delete all unwanted cookies in order to help protect your privacy.
YouTube5, Chromed – Forces YouTube videos to play in HTML5.
I hope someone has found at least one of these extensions to be useful. If you have any favorite extensions feel free to list them in the comments section.