X-33
NASA announced March 1, 2001, that it would not add Space Launch Initiative funds to the X-33 program. As a result, the X-33 program came to completion when the cooperative agreement between NASA and Lockheed Martin, expired on March 31, 2001.
For more information:
http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2001/01-062.html.