Best tool to check Google page rank is Google Toolbar. These days Toolbar is not compatible with latest version of Mozilla so you need to work on older mozilla or you can use IE 8 instead.
The site you are on has the world's largest historical rank tracker: http://tools.digitalpoint.com/tracker.php (about 100,000 people use it)
I use SEO Powersuite Rank Tracker Enterprise. Nothing compares from this tool. Although ranking reports may vary from actual search from 1-2 spots.
I use my own bulk pagerank checker tool here http://www.bulkseotools.com/ - You can do bulk check pr of 500 urls and no need to enter so annoying captcha.
If you mean your rank in the search engines - I use market samurai to track. Also Paul Forcey's plugin. For PageRank I use the SEO for Firefox plugin I prefer it to SEOQuake coz it seems more reliable.
Hi to all . I have nothing against to all free rank checkers, but...i saw they are not that accurate in results, as i though. If i am wrong please come up with an argument/s. Also i am curious why many people are doing so regular confusing between google adwards results ( which are for adsense campaings ) and the results for competition level by results in google - which are totally different by the results from google adwards, are one and the same thing for some people. !!?! They think if the local results on google adwards is low - same sould be the work to rank it on Top 3, for example, where the google results are few millions... Hope i am clear enough on this..