The main ones you really need to worry about until 70 are :-
Jerkin of the Untamed Spirit - Hellfire Peninsula Quest
Manimal's Cinch - Shadowmoon Valley Quest
Verdant Gloves - Shadowmoon Valley Quest
Socrethar's Girdle - Netherstorm Quest
Ash Tempered Legguards - Shadowmoon Valley Quest
Supple Leather Boots - Blade's Edge Mountains Quest
These are all items that are good even after 70. The boots, legs and chest can all be replaced at 70 by the
Heavy Clefthoof Set which are now fantastic tanking items.
Everything else can be farmed from instances in the Outlands or will be replaced very quickly from quest rewards in the Outlands as you level. That's right, don't worry at all about your gear at your level. Just take whatever quest rewards or drops come up and concentrate on doing the quests and leveling rather than farming for items that you will replace in a few levels anyway.