How to evaluate how good a tagger is

I've almost completed writing a new part-of-speech tagging 

scheme. My problem is how to evaluate how effective it is  

at tagging. What's the best way of doing this at the moment?               

I have a copy of the Susanne Corpus, and I'll definitely   

use that in my experiments. What other tagged corpora      

are out there? (Either public domain or can be purchased). 

Are there any other good methods of evaluating how good    

a tagger is?  


Bill Teahan