C-SPAN and StreamSage (the folks behind CampaignSearch) have just made available the chance to keyword search the audio of the first presidential debate, find results, and then click to view the section of the debate where your search terms are spoken. StreamSage uses voice recognition technology. It's not perfect. I would expect that the other debates will be available. To access material:
1) Enter Search Terms
2) Click search
3) Sort results by date, the link to do this is right below the search box
4) Select results and watch video segments with RealPlayer
5) This database contains more than material from the first debate. C-SPAN's "Audio Track Search" contains 175+ hours of keyword searchable C-SPAN content.
Speechbot, from HP, also uses voice recognition technology. This database contains nearly 15,000 hours of keyword searchable radio material.