A hundred years ago the only way someone could see what was going on in Congress was to visit the city of Washington. Now, thanks to the wonders of modern technology - events can be followed from almost anywhere in the world.
C-SPAN has the most important audio-visual feed. C-SPAN 1 brings live coverage from the House of Representatives, while C-SPAN 2 deals with the Senate. These, and other C-SPAN channels, broadcast 24 hours a day. If you haven't visited the website - it's worth going to.
(Some) committee Hearings can be viewed live at http://www.capitolhearings.org/.
Both House and Senate websites are useful for keeping up with events