Gathering materials are a decent way to earn some money, just send your companions out to gather materials and sell them on GTN. The place is full of lazy crafters who dont want to gather themselfs:p
I always do this while leveling and can buy what i want on the GTN with the credits i earn. For example, i just started a Shadow (Scavenging, Underworld trading and slicing)and i am lvl 20 right now with 250.000 Credits burning in my pocket.