OK, there's a mountain of footage out there, but I hope I'm not boring anyone by drawing your attention to a couple I've come across recently that stand out, for me anyway?!
Firstly some footage from last years TT. Great onboard footage in 720p and it's not often you get two evenly matched riders circulating like that, so you have both 'cockpit' view and 'chase' view at the same time. Watch at 1min50 for cement dust being thrown in your face just as you tip in to a 170mph blind right hander! Also at 3mins11 you might be able to pick out me and my Dad sitting on the stone wall on the left!!
http://www.youtube.com/watch?v=FOTEVXeLDHA&feature=player_embeddedAnd then this is from the 1997 NW200 in Northern Ireland. Best head cam footage I've ever seen. It really gives you an appreciation of how the riders get battered around by the bumpy public road surface. Also it's amazing to think that this is in fairly damp condions!!
http://www.youtube.com/watch?v=u8aAGiE0arw&feature=player_embedded