I just finished watching all but the first few minutes of the Conyers hearing (on C-Span); it was more than two hours long, and was well worth watching. The prepared statements by each of the committee members were well thought-out, and provided a diverse array of viewpoints on the implications and context of the Downing Street Minutes. The meeting got even better during the question-and-answer period, when the dozens of Congress members in attendance asked each of the committee members pointed questions; the committee members gave candid answers to all questions asked of them, and clearly elucidated why the Downing Street Minutes warrant further investigation by Congress. I urge you to watch or listen to the entire meeting if you can.
C-Span 2 will re-air the meeting in full today (Friday, June 17) at 8pm EST.
I still haven't found an online transcript or complete video of the meeting, but I have found a few more resources:
Downing Street Memo Video Highlights - post by Crooks and Liars with a few video highlights.
Bush pressed to answer `Downing Street Memo' questions - Knight Ridder story on the hearing.
Bush policies blocked as US mood on Iraq sours - an article in The Independent which discusses the Downing Street Minutes in the context of other events occurring in Washington.
A Democratic Underground thread contains pictures of the hearing (apparently from the AP).
Google News has a bunch of stories related to the hearing, but most of them are short summaries that simply rehash much of what has been said in my prior links.