as the title says, this is theory but I have got 48k armor before, the problem is though, it only lasts for about 2 secs and you need lagg. Maybe someone could get around this and keep it forever so you have more armor than you're meant to...
What you need
At Least: a lvl 40 druid with all points in balance
Moonkin Form
Dire Bear Form
A little bit of lagg
What to do
Create some lagg, I usually do this by downloading about 10 1gig torrents at the same time but you can do it any other way
Go into Moonkin Form
Open character info (press c)
Go into Dire Bear Form and enjoy your 2 seconds of improved armor!
My stats when I did it
Lvl 70
3k armor out of form
12k armor in Moonkin form
48k armor IN BETWEEN Moonkin and Dire Bear
then back to 12k a second later in Dire Bear
The main reason I'm posting this is coz hopefully someone reading this will know how to make it permament and share it and perhaps this will be repeatable to the extent that you're invincible (sorry getting my hopes up :P) and will be able to solo instances quite easily
EDIT: forgot to mention, this works on live (I was on 2.4.2 when I did it but it shouldn't have changed anything)