The base spirit maximum of 150 is pretty low if you actually want to use those spirit-consuming skills frequently. It can happen easily that you don't have enough left when you're trying to use the more expensive skills for 50 or 75 spirit.
The only way to increase the maximum spirit I've found so far is the "Exalted Soul" passive skill, which increases it by 100.
Are there any other ways of increasing the maximum amount of spirit for a monk?