I've just recently come across an interesting tool available at seomoz. The page strength tool is designed to give a more thorough analysis of the importance of a page than the google pagerank.
It looks at a host of factors, including the google pagerank, to give a more detailed and more up-to-date analysis of a page. It takes a bit longer to gather the data (there are more sources to query) but I think it is a more useful tool than just looking at the google pagerank.
We really rate this tool, although our page strength is ostensibly less than our Google PR, we think it probably offers a more 'balanced' assessment of the sites worth and of course it keeps us on our toes.