As a semi casual, you can get pretty darned good tanking rings through quests - Ring of unyielding force just isn't that great of an improvement over other available rings (it is better yes, just not THAT much better).
You won't go wrong with [item]Brooch of Deftness[/item] or [item]Bracers of the Ancient Phalanx[/item]. Both are pretty much unreplaceable. Think about [item]Slikk's Cloak of Placation[/item] as well. If you are just doing heroics for badges, those are 3 cheap and incredible upgrades.
The beast is getting hungrier.