I just made 80 too. My pally tank only has 525 Def - trying to find more... but where?
I have about 21K hp and 22K armor

I also have a resto shammie and 3 ele shammies all of which have about 2000+ spell 14.5%crit and not very good spell hit.

I have tried 4 heroics... Gundrak, UK, Violet, and Drak-Tharon - I managed to get two badges... off the mammoth guy in Gundrak and the prince in UK.
Everything else rocks me.
Gundrak:
The snake guy in Gundrak, constrictors stun my tank and its over for my DPS.
The stone guy in Gundrak walks on me. The elemental he turns into destroyes the Earth Elemenetals and then the water pools drown my DPS (not like the wiki says) on Heroic.
UK:
I have found pulling the prince into the room before his - hidding in a corner at the top of the stairs worked best.
Drak-Tharon:
The shadowmages suck the life from you quickly - I died a wipped a few times on them... kill/hex/stun them fast
The first boss gets stronger - DPS race, before he 1 shots your tank... I cannot see to win

Get/buy/steal as much gear as you can before you try any heroic. Use well fed food, get flasks or something.

They have left a sour taste in my mouth