Blacksmithing can make you some very good bank ... if you do it smart.
Not much of what you can make will sell, generally avoid crafting anything other than whites, whites have a chance to create Green or Blue, a high dura version of either can sell well enough to put on the AH.
Generally however, I stick to shields. They sell VERY well to vendors, so much so that @ 56 I'm still crafting a 47 shield since I can buy all the matterials off the AH, and still make $ just by vendoring 100's of them. If I create an especially good one it goes on the AH for a reasonable price and sells pretty well.
That said, post 47 the shields available all cost MORE to make, thus I'm stuck crafting 3000 shields for a single level. The good news is it's free $ while I go AFK for a while.