PageRankSharp is a small .Net library to check the current Page Rank of an url. There is also a command line version that works on Windows and Linux/OS X with Mono.
You can download the console utility and the library here.
The source code is licensed under the MIT license.
The source code is hosted (and can be retrieved for free) at http://github.com/alexmipego/PageRankSharp.
To use the library simply add a reference to your project and get the Page Rank with something like this:
int rank = PageRankChecker.CheckUrl("www.google.com");