The big main press conferences are up on game trailers, there is also the IGN verison that look like the same feed but they are on youtube, so which ever version suits you. Youtube versions are listed last
Microsoft E3 2011 press conference
http://www.gametrailers.com/video/e3-2011-microsoft/715731
http://www.gametrailers.com/video/e3-2011-microsoft/715725
http://www.gametrailers.com/video/e3-2011-microsoft/715723
http://www.gametrailers.com/video/e3-2011-microsoft/715721
http://www.gametrailers.com/video/e3-2011-microsoft/715719
http://www.gametrailers.com/video/e3-2011-microsoft/715715
More from Sony, Nintendo and the rest after the continue reading
Sony E3 press conference
http://www.gametrailers.com/video/e3-2011-sony/715655
http://www.gametrailers.com/video/e3-2011-sony/715657
http://www.gametrailers.com/video/e3-2011-sony/715659
http://www.gametrailers.com/video/e3-2011-sony/715661
http://www.gametrailers.com/video/e3-2011-sony/715663
Nintendo E3 press conference
http://www.gametrailers.com/video/e3-2011-nintendo/715574
http://www.gametrailers.com/video/e3-2011-nintendo/715584
http://www.gametrailers.com/video/e3-2011-nintendo/715586
http://www.gametrailers.com/video/e3-2011-nintendo/715588
EA E3 press conference
http://www.gametrailers.com/video/e3-2011-electronic-arts/715597
http://www.gametrailers.com/video/e3-2011-electronic-arts/715599
http://www.gametrailers.com/video/e3-2011-electronic-arts/715603
http://www.gametrailers.com/video/e3-2011-electronic-arts/715665
http://www.gametrailers.com/video/e3-2011-electronic-arts/715669
http://www.gametrailers.com/video/e3-2011-electronic-arts/715673
Ubisoft E3 press conference
http://www.gametrailers.com/video/e3-2011-ubisoft/715677
http://www.gametrailers.com/video/e3-2011-ubisoft/715689
http://www.gametrailers.com/video/e3-2011-ubisoft/715679
http://www.gametrailers.com/video/e3-2011-ubisoft/715685
http://www.gametrailers.com/video/e3-2011-ubisoft/715681
http://www.gametrailers.com/video/e3-2011-ubisoft/715687
the same again from youtube
microsoft
part 1 http://www.youtube.com/watch?v=77c2S0V4__w
part 2 http://www.youtube.com/watch?v=V0l9H0gRlXM
part 3 http://www.youtube.com/watch?v=F0LTmJWkqFs
part 4 http://www.youtube.com/watch?v=CXGPDJXMdws
sony
part 1 http://www.youtube.com/watch?v=FuZBYuRHZrs
part 2 http://www.youtube.com/watch?v=OuryrgGVGJQ
part 3 http://www.youtube.com/watch?v=rg1OfvU-1W8
part 4 http://www.youtube.com/watch?v=Y2tjhXAoVBU
EA
part 1 http://www.youtube.com/watch?v=vSoMfutC9eU
part 2 http://www.youtube.com/watch?v=kFLGrex4wRo
part 3 http://www.youtube.com/watch?v=2UqUt1rgvJk
part 4 http://www.youtube.com/watch?v=GFPk-hDItP4
ubisoft
part 1 http://www.youtube.com/watch?v=SGFVza69fCs
part 2 http://www.youtube.com/watch?v=XSzyp78MWWM
part 3 http://www.youtube.com/watch?v=pq763VGBa5M
part 4 http://www.youtube.com/watch?v=3UxiJ_D7n9Y
nintendo
part 1 http://www.youtube.com/watch?v=_DeQUW-bFZ0 //all about zelda
part 2 http://www.youtube.com/watch?v=E9IipwmRJfU&NR //3ds stuff, mario kart, mario brothers, star fox, kid icarus
part 3 http://www.youtube.com/watch?v=GBKrD64DTH4 //luigis mansion, 3ds eshop, pokedex, virtual console, wii u haha
part 4 http://www.youtube.com/watch?v=mCHuiOmOwKY