I've tried a couple tools online that try to predict the Google PR you will receive in the next Google PR update, with completely different results. Can someone recommend a reasonable accurate tool for predicting Google PR, I'm mostly just currious what they say about my site?
One does not exist. All of them predicted incorrectly for some sites on this past update. You're just as well off making an educated guess yourself...
My advice will be not to get addicted to such prediction tools, they can never be accurate and stop worrying about PR. Just look to acquire more and more quality and theme based links.
PR prediction tools must be based on your previous work until the date you use the tool, and this is just you saw from google toolbar. But between the date you use the tool and the date google update PR, it's still a long time and there are a lot of works you can do to increase your PR. So I think PR prediction toll is just a measurement of your current PR, and for future PR, even google can't predict it for you.
I used to own a website that could read off Google's datacenters called futurepagerank.net. It was quite accurate and naturally, became popular among webmasters. Soon after that, Google did something and none of the pagerank prediction sites could read from Google's datacenters anymore - including iwebtool. (FYI, I no longer own futurepagerank.net)