FORA.tv
Fora.tv streams selected events, e.g. conferences, interviews. Sometimes these are available live (some free). There is also a large library of past events from conference partners, including the Aspen Institute, the Economist, and the Hastings Center.
TEDLive
"TED is a nonprofit devoted to spreading ideas, usually in the form of short, powerful talks (18 minutes or less). TED began in 1984 as a conference where Technology, Entertainment and Design converged, and today covers almost all topics — from science to business to global issues — in more than 100 languages. "
Includes live streaming and on-demand.
The library subscription database, Films on Demand, includes selected TedTalks. Use this when you--or your students-- need special tools, such as the ability to show a single segment, create a playlist from segments, customize a segment, or view a transcript. 
Conal: Conference Alerts is a database of scholarly conferences around the globe. Search by discipline, date, or location.
Many conferences keep an archive of their conference agendas; some keep an archive of abstracts or even papers. If they still produce it in print, most will have information on the title so that you can find it in Worldcat.org and order a copy our Interlibrary Loan service.