Many NPR stations will be broadcasting up to 4 hours coverage each evening (US time) - you can listen via http://www.npr.org/templates/player/mediaPlayer.html?action=3&t=live1&islist=false or through a local station "listen live" - see the list at http://www.npr.org/stations/
C-Span will be providing extensive coverage at http://www.c-span.org/Watch/C-SPAN_wm.aspx
Other Major News Sources
http://www.demconvention.com/ - an official site. Worth looking at Convention 101 and Countdown to America's future.