Screw the Firefox people! For those who use the One True Browser to Rule Them All, what are your favorite extensions? I have some amazing ones, starting with:
Chromey Calculator - calculator add-on powered by Wolfram Alpha. It doesn’t take every single search string that works in WA, but it will do most of it. And if you don’t already know about the mind-boggling computational power of WA, you haven’t really lived…
Google Dictionary - too cool for school, this extension lets you double click any word while you are browsing to get an instant definition. I use this on a daily basis.
Invisible Hand - whenever you are shopping online, it will slap an unobtrusive bar along the top of the screen to let you know where you can get the same item somewhere else cheaper. If you’re really paranoid about people snooping on your buying habits it might not be for you, but I trust them for no other reason than the fact that I stopped giving a shit about marketers spying on me a while ago. Plus they say they don’t store any info, and why would they lie? 
Google Mail Checker - very simple but very useful: shows you when you get an incoming mail to your Gmail account immediately with a little number indicating the number of unread messages in your inbox. There are similar extensions that do the same thing with more features added in, but this one suits me fine.
Readability Redux - renders pages such as news articles without all the junk around the fringes and just gives you straight, beautifully legible and readable crisp text in the font and background color of your choosing (it will also include any images that are in the article itself, but none of the ads or extraneous images in other frames). Simply marvelous.
View Thru - shows you the URL where a link that’s been shortened by a link-shortening service actually goes to on hover-over. I got paranoid about shortened links from my days of surfing the WoW forums, where keylogging Chinese hackers frequently posted fake links using tinyurl to obscure the fact that they were actually sending you to xxxhackurshit.cn/fuckyou.exe.
AutoPager - *caveat: I’m very ambivalent about this one since the options are garbage and frequently don’t work, but the extension itself is great for reading stuff that requires you to page through multiple pages. Instead of clicking to go to the next page and having everything refresh, it will render the next page on the fly as you scroll down.
AdBlock - goes without saying (and I believe it’s the same as the Firefox add-on by the same name), but I’ll throw it in here for the sake of thoroughness.
Well, I have a few more but those are some of my favorites. Share any other awesome extensions that you use.