Here is a list at where you can watch E3 for each press conferences
EA's live strea is on Monday, June 4th, at 1:00 PM PST You can catch it on their website.
Ubisoft's live stream is on Monday, June 4th, at 3:00 PM PST. You can catch the stream on their uplay website. Ubisoft's will also be live streaming their games over the span of E3
Sony's live stream is on Monday, June 4th, at 6:00 PM PST. You can catch the stream on their website.
Beyond the conferences you'll be able to watch live streams of various things at E3 on the following websites. Some may consistently live stream while others may only do it for select things.
Some of them are also live streaming the Main Conferences
Uplay. A stream of select Ubisoft titles at various times during E3
IGN As a bonus, IGN will also be live streaming through their Xbox Live App.