Before going further, note that both Blackboard and WebCT incorporate assessment functionality. Below is an overview of one other commercial assessment tool:

TestPilot from Clear Learning consists of a database of test, tutorial, or survey questions and a Web server extension to both administer the assessments and record, score, and retrieve user responses. It's available for the Macintosh, Windows, and Unix platforms. You can try out the product for free on Clear Learning's own server. All you need is a Web Browser (4.0 and higher).