Following a lead from slashdot I've found a free lecture archive on audible.com that includes the Library of Congress Series on the Digital Future, which features presentations by David Weinberger and Larry Lessig, among others. Not only is it free, but due to audible.com's Red Tag Sale, it's also 50% off! What a deal!
ps. I don't know if audible.com allows deep linking, if it doesn't work, do a search on audible.com for Lawrence Lessig, click on the Library of Congress Speech, then click on the link to C-SPAN on the speech page, then click on See All Matches.