For the past 8 months I have been developing WeBWorK into Moodle. The final result is a plug-in in the form of a question type for Moodle 1.8.x. The application has been deployed at the University of Rochester.
The main site is: http://question2.webwork.rochester.edu. You can find more information about features and installation there.
Any feedback would be immensely appreciated.