You probably know about PodZinger, which does machine transcription of podcasts and makes them available in a search engine. I came across CastingWords, at http://castingwords.com/, which doesn’t do machine transcriptions but does have a search engine.
Two interesting things about this site. First it offers a podcasting transcription service — podcasts transcribed by humans — for 42 cents a minute. (Uploaded file transcription is available for 75 cents a minute.) Uploaded podcasts which are transcribed are made searchable via the query box at the bottom of the front page.
Second interesting thing? The transcriptionists are being found via Amazon’s Mechanical Turk! See the FAQ for more details. Jeff Barr walked through the process of buying a transcript and posted his experience with many screenshots at http://aws.typepad.com/aws/2005/12/walking_through.html.