Question about quests

I am currently at Thunderhead Keep, and I have no more quests to do on my quest log. I traveled everywhere, just about, hoping to find a few new quests...but found nothing new. I doubt I could have done EVERY quest with my ranger already. Do more quests open up in places after you finish the final mission?

Short Answer: Yes, Some new quests open up after you finish the final mission.

Note: Thunderhead Keep is nowhere near the final mission.

Thunderhead Keep mission will teleport you to Perdition Rock. There are 3 missions and a number of quests there to do too.

By "number of quests" you mean ONE quest. >_>

(The quest that directs you to Ring of Fire)

Not true, not true at all...!
New quest will appear in Droknar's Forge after you finish te last mission in the Ring Of Fire. Kneel for the vision of Glinth, she will give you one new quest. When you finish that quest you will "earn" 3 new quests. When you finish those 3 you finished all the quests (that are always avalible).
*Remember* there are quests in the UW and FoW.