Chrome: Gmail has great integration with Google Drive for cloud storage, but the feature is useless if you don't use the latter. Cloudy is an extension that adds attachment support for Dropbox, Evernote, Facebook and more.
Click the attach button from the compose view, and you can select files from any of your cloud services or social networks. The file then gets attached to the message just like any other attachment.
If you have files spread across multiple services, Cloudy makes sending them off as an attachment in an email a simple one-step process.