pre raid you want as much 346 ilvl tanking pieces as you can get. rep grinding hyjal, ramkahen, and dragonmaw/wildhammer should be your first few goals to get the 359 ilvl cloak, bracers, and boots that will last you until heroic raids. you can wear a few hit/mastery and/or expertise/mastery pieces if you feel like you need some threat stats for heroics.
there is no real bis pre-raid tank set since there are many different pieces you could get for each slot from justice points and heroics to get you through the first couple of raid bosses. the blacksmithing crafted shield i would say is a must have since it's not too expensive by now and will last you until heroic raids as well. i wouldn't waste gold on the crafted chest or belt though since your first valor purchase should be your tier chest and there are tanking belts that drop off the starting raid bosses.