Not that you will be asked every day at the reference desk where on the Internet someone can locate sound samples, but in case someone does you can use a search engine for sounds called FindSounds.
"Each month it processes more than one million sound searches for more than 100,000 unique visitors. Since its debut on August 1, 2000, it has processed more than 35 million sound searches."
You can search FindSound by using different keywords or clicking on one of the 500 preset sound categories like "people", "Tools", "Animals" etc.
Users could also specify file format ( Aiff, Au, Wave), mono or stereo channels, file size and resolution ( 8 , 16 bit).
Via: Sites And Soundbytes