You basically can't get an upgrade until you're 80. If you're leveling, then the starter one is your only option. Once you hit 80 you can get a couple from badges, but the best one (imo) is in naxx.
2 of them are pretty good (203 damage to scourge strike for one, 203 damage to icy touch for the other). I don't remember why i didn't get the 3rd one...it wasnt good in my opinion (as a level 80)