ArsElectronica 2005 (1st-6th September) titled »Hybrid — living in paradox« has published most presentations as audio. There is a link »Webcasts« in the navigation, but it doesn’t contain any content yet.
ArsElectronica has now a history since 1979. I’ve been to it in 1995 and it was quite an inspiring festival. I really think it is great they offer all their festivals in their archive (and even webcasts since last year’s festival).