In Game Update 2.0, certain Legacy Achievements grant Cartel Coins. They only grant once per Legacy, so it's not a feasible way to get a lot of them for free, but it's kind of cool.
From the official SWTOR blog (emphasis mine):
This update also includes an all-new Achievements system. Starting in Game Update 2.0, players will be able to earn Achievements for all sorts of activities in-game, including crafting, exploring and unleashing their wrath on the world around them. Over 1,900 Achievements are in this release, and we see the system as a great way to add more, and more varied gameplay in future updates. Achievements can also grant rewards such as titles and in some cases Cartel Coins.
Currently you can get a total of 860, as per Dulfy.