I'll reprint what I wrote in the first Monk/Shield thread.
Well, there are at least a pair of shields that monks should (in a perfect world ) be able to use:
1) Rattan Shield- The woven rattan shield is a staple of Southern style Kung-fu. It's very lightweight and steeply rounded (almost the exact shape of Captain America's shield) and designed to actually AID martial artists in tumbling to close with long poled weapons (specifically spear and tiger fork). The shield and butterfly sword set is a famous one in Hung-gar style.
2) Paired Tiger Steel Shields- Very rare. These are lightweight, narrow (1' wide, perhaps 3' long) shields that are used as both weapons and shields. They come to a long, razor sharp spearpoint that projects perhaps 6" past the hand and are used to stab.
Do I think monks should be able to use normal shields? Probably not, simply for game balance reasons. Should they be able to use Rattan shields and Paired Tiger Steel Shields? Sure, with the appropriate EWPs, as Paired Tiger Steel Shields especially are practically the textbook definition of a Exotic Weapon.