I'm building a tanking Monk, however I have not yet found a shield worth using.
I find that the faster spirit generation caused by duel wielding (increased attack speed = faster spirit generation) is better than a little extra armor or chance to block < 1000 damage.
Since there really isn't a concept such as aggro, tanks need to be more than just damage soaks. They need to be able to control mobs, and keep them away from the squishier members of the party. To me, having faster spirit generation to control the mobs and keep them away from my allies seems more important than a little extra armor and block chance, providing my other gear provides me with enough stats to survive.
The best shields I've found so far have been about 1400 armor, and typically have < 20% chance to block a few thousand damage. The extra armor doesn't seem to be enough to be worth it, and the amount blocked seems too low to matter. If something is going to kill me, it hits for quite a bit more than 1k-2k.
But I am not sure if this will hold up in the higher difficulty levels.
Can I be an effective tank as a Monk without a Shield at higher difficulty levels?
It should probably be noted that I don't ever play my Monk alone, and this question is about being a tanking Monk as part of a group, not a tanking Monk playing solo (My current build is here)