I've just come across a very simple Perl script that allows you to monitor your Google PageRank through an RSS feed. While I don't know why anyone would actually want to monitor such a thing (*cough* you can find my feed here), the idea is still pretty neat and a much better solution than using those "pagerank calculator" sites to check it manually (again, who does that? :P). I realize that I could get this information through the Google Toolbar, but that requires both Windows (which I don't use) and Internet Explorer (which you couldn't pay me to use; well, maybe if you paid me a lot and I didn't have to actually be connected to the Internet while it was open).
If you are looking to setup a feed for yourself, use this site to calculate the checksum value you'll need (the site linked to in the original article no longer exists and so I had to find another one).
One could obviously take this simple code and port it to many other languages to provide similar solutions (e.g., maybe a shell script that would check for a change every hour and then e-mail you when a change is seen), but RSS is the way to go for me.