9-11 Commission hearings at Audible.com (free!).

The list has been updated to include:
Thomas J. Ridge (5/19/04)
NYC Panel Two (5/18/04)
Staff Statement No. 14: Crisis Management (5/19/04)
Michael R. Bloomberg (5/19/04)
NYC Panel Four (5/19/04)
NYC Panel One (5/18/04)
Staff Statement No. 13: Emergency Preparedness (5/18/04)
Rudolph W. Giuliani (5/19/04)
NYC Panel Three (5/18/04)
John Ashcroft (4/13/04)
Panel: Summer 2001 (4/13/04)
Staff Statement No. 10 (4/13/04)
Staff Statement No. 11 (4/14/04)
George J. Tenet (4/14/04)
Panel: Preventing Future Attacks (4/14/04)
Panel: FBI Leadership and Initiatives Post 9-11 (4/14/04)
Staff Statement No. 12 (4/14/04)
Janet Reno (4/13/04)
Staff Statement No. 9: Law Enforcement (4/13/04)
Louis J. Freeh (4/13/04)
http://www.audible.com/adbl/entry/landing/911Hearings.jsp?BV_SessionID=@@@@0847105620.1085132822@@@@&BV_EngineID=ccccadclidfhjkicefecegedfhfdfok.0

You can listen to them online, download them into your HD for later listening, or load them into many popular PDAs (iPod also).

pnorman