If you select one or more files in the Finder, right-click, and use the Share option for a service like Flickr or Twitter, your files will animate into the share sheet that appears.
Bonus tip: to add accounts to this Share menu, go to System Preferences > Mail, Contacts & Calendars, and scroll through the list of account options on the right.
Bonus bonus tip: Finer Things in Tech is now a YouTube channel, if you’re into that sort of thing.