Since SWTOR's 1.3 patch, I have been working on an in-game project. The goal: Earn 1 million credits by playing the Auction House. I'm happy to say that I reached this goal a couple of weeks ago. It turned out to be pretty quick and painless too.
This was all done on my level 31 Jedi Knight (I still don't have a 50). The basic idea is just to buy low and sell high. The other big money-maker is the Slicing crew skill. Crew Missions are very valuable, especially Slicing ones due to the new patch.
There are a few other items you can buy and sell, but I'll leave that as an exercise to the reader. One million credits really is not all that much if you look at some of the legacy prices, but it is nice to have going forward. Not sure I am going to try for 2 million, might wait for the next patch.