Chrome: Tab Grouper is a simple extension that does one thing: groups all your tabs from the same site together, so you don't have to go searching through your tab bar to find the right one.
Some sites just beg to be opened in numerous tabs. Whether you keep finding interesting things on Wikipedia, loads of funny videos on YouTube, or handy how-tos at your favourite tech blog, Tab Grouper will make sure they're always grouped together in your tab bar and then sorted alphabetically by site. I wish it had a few options, like the ability to exclude a domain from being grouped, but it's hard to argue with something so simple. If you don't already obsessively organise your tabs just so, this is a great extension that can make browsing a bit easier.
Tab Grouper is a free download, works wherever Chrome does.