See the image below for how it should have looked. In my case, I didn't see any of the options in the third section - ie. those with the Dropbox symbol on the left.
Given that I regularly 'Share' Dropbox files and folders from Finder, this was a real pain!
To resolve the problem, I needed to download and install the latest version of Dropbox (which, as at 30/10/14, is 2.10.41) and re-install. Here is the link to the page that will download and install the latest Dropbox version for you.
You don't have to uninstall your existing Dropbox first - the installer will replace it for you.
Then, re-start your Mac and your options should re-appear once Dropbox 'fires up' after the restart.