http://dulfy.net/2012/10/23/swtor-cartel-market-items/
Write up on what you can buy... To spend cartel coins you do not have to go to the store, the store is on your UI. However, I would wait, there are some reports that they are subtracting too many coins for a purchase at the moment and other reports that people buying cartel coins form the website are not get credited for the coins. Day 1 patch buyer beware.