FindSounds.com

The Internet has an increasing number of specialized search engines, but this might be one of the most unique. With it, you can search for various on-line sounds. Common search words like "cat," "dog" and "baby" returned 200 hits, which would seem to be the maximum it returns. Conceivably, one could use one of the 113 files found by searching for "applause" to spice up your lecture.

http://www.findsounds.com/