Outland is fairly neatly organized. You never have 3 different zones to visit for a certain level range, its usually best to stick to a single zone and move to the next when you're done there. It progresses as such;
Level 60-70 questing
Hellfire Peninsula (61-62)
You arrive here when you enter Outland through the Dark Portal in Blasted Lands. The quests will let you either reach 62 or very close to it. The Ramparts and The Blood Furnace instances are in this zone and good for this level range.
Zangarmarsh (62-64)
When finished in Hellfire Peninsula, you will be heading to Zangarmarsh. Quite a change of scenery, this zone will hold you over until at least 63, perhaps 64 depending on rested experience, whether you did any instances or not and whether you skipped any quests or not.
Instances for this level range within the zone are The Slave Pens and The Underbog.
Terokkar (64-66)
Next on the list is Terokkar, instances for this level range here are Mana-Tombs and Auchenai Crypts. Sethekk Halls is a possibility too, but is a little high level for a 66 player.

Nagrand (66-67)
Nagrand is home to no instances, but this level range is quite fine for some of the Terokkar instances, if you missed em.
Blade's Edge (67-68)
No instances again, but plenty of questing to do.
Netherstorm (68-69)
Netherstorm has Tempest Keep in it, a four instance flying fortress. One of them is a raid zone, but the other three are 5 mannable. They're all a minimum level 70 (68 for druids) though, as you require a flying mount to reach them.
Shadowmoon Valley (69-70)
you may have hit 70 in Netherstorm already, but you can finish up in Shadowmoon if not. Even if you are, questing beyond 70 is worth a lot of gold.