Shortly after Google Chrome's Extensions gallery opened, we rounded up 18 worthy downloads. Now that Chrome's official add-on market has matured a bit, we've dug up more productive, annoyance-fixing, feature-adding extensions that you should consider adding to your collection.
At this point, extensions for Google Chrome work on the Beta and Dev channels for Windows, the Beta for Linux, or the dev channel for Macs. If an extension doesn't work across all platforms, we've noted it at the front of each description.
Checkers & notifiers
• Google Mail Checker Plus: There are tons of Gmail and Google Apps checkers in the extensions gallery. So why this one? First off, it handles both standard Gmail and (multiple) Google Apps accounts. Second, its roll-down mail notifier lets you actually act on the messages it shows—archive, delete, spam, mark as read, or reply. Third, if you don't ever want to open the Gmail tab, that's fine—you can read the whole message in the checker window. Fourth, and finally, it offers a wide range of icon styles to choose from, so it meshes with whatever Chrome theme and OS you've got going. Best of class.
• Google Calendar Popout:As with Google Mail Checker, this is one of many Google Calendar extensions to choose from. The version made by Google offers a little button badge showing you the time until your next appointment, but for those with multiple calendars, it's a bit annoying, because it only picks up appointments from the primary/personal calendar. This model simply rolls down a mini-calendar (which you can turn off in the options), shows color-coded appointments, and offers the Create Event and Quick Add links that GCal addicts depend on.
• One Number: 
This one's simple. If you're a Google fiend who doesn't want blow-by-blow pings and notifiers, One Number combines all your Google app notifications into one handy window. (Original post)
Annoyance fixers & site improvers
• Better Gmail:
Our own How-To Geek had previously rounded up a Better Gmail for Chrome to complement the popular Firefox extension, but Chrome's extension system and script support has changed quite a bit since then. A very helpful coder rounded up scripts that are still working into another Better Gmail extension, one that includes a lot of the things we like to see available: folder hierarchies, mouse-over row highlighting, footer appending, and much more.
• Clickable Links:
Forums, blog comments, really old sites—they're full of links written out in text, asking the reader to precisely copy and load the text in their address bar. This extension updates those annoyingly non-interactive links to the modern day.
• A Bit Better RTM: 
It simply tweaks, improves, and makes shortcut-friendly the Remember the Milk webapp for the convenience of serious task management. Based on the popular Greasemonkey script, Bit Better moves your list tabs to the left, lets you hide lists you hardly ever look at, and makes nearly every action do-able from a keyboard. It does those things and more from the background, too, so that's one less taskbar button to deal with. (Original post)
• VidzBigger: This two-for-one add-on reconfigures the layout of YouTube, MetaCafe, and DailyMotion to make the actual videos the (larger) star of the page, and also adds a download link whenever possible to your viewing screen. You can also scroll related videos without having to move your video out of place, which is just the thing for ... terribly unproductive web video binges. Sigh. (Original post)
Other cool stuff
• IE Tab:
Windows only: As you might expect, IE Tab isjust like its Firefox counterpart: It renders the web page you're looking at in a separate tab, using Windows' built-in Internet Explorer rendering engine. Helpful for developers, and those 476 remaining sites that refuse to accept any browser except IE.
• Session Manager:Chrome can automatically pick up your tabs where you left off, and offers a decent tab and web history from its "new tab page." If you tend to open tabs in batches, though, or don't always want to pick up exactly the way you left it, adding Session Manager to Chrome is a nice time saver. Open up a batch of tabs, save them to a new session name, and you're up and running. (Original post)
• Everymark: An extension after our own hearts, mostly because these hearts love the light-speed-quick Everything search engine for Windows. Everymark aims to provide that same type of as-you-type convenience for your local bookmarks. Chrome's own OmniBar (that's "address bar," for those who don't buy into Google's super-hype terminology) does a decent job of pulling up bookmarks that you're typing for, but Everymark searches the name, the URL, the date modified, and folder names, all at once.
• WOT (Web of Trust):
This one showed up in early form, but now ranks as one of the best sanctioned extensions to tell you more about where you're going on the internet. Using WOT's research and input from the community, the extension shows you the trustworthiness of whatever page you're looking at, and provides a link to the rating page with more information.
• Firebug Lite: 
In the hearts and minds of developers who love Firebug, nothing can replace it. But this is a noble first attempt for the Chrome-using set. It comes from the same development team, and it's basically a JavaScript file, molded into an extension, that emulates some of the Firebug features that let you watch in real time as you change a site's code.
• uTorrent for Google Chrome: Are you a uTorrent fan who's also a Chrome user? Install this little add-on to your browser and, using the awesomeness of uTorrent's WebUI, you can remotely control your BitTorrent downloads from anywhere in the world (that has web access). uTorrent itself is only for Windows and Mac systems right now, but this extension can be used anywhere Chrome extensions are allowed.
What extensions have made their way into your must-have list, or just your Chrome taskbar for now? Tell us, and link, your favorite finds in the comments.
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