Term Extraction Tools

Revisiting my long dormant toy that uses analysis of song lyrics and Flickr or Google Images to do contextual visualizations. I have implemented a simple ti.idf frequency counter and am getting decent results but wanting for more. In this web 2.0 world maybe I should be looking for services to do this?

Consider:

Yahoo Term Extractor API
Topicalizer
OpenCalais
Alchemy

and mabye Wordnet for synonyms.

Also, possibly relevant is Echonest's colossal db of music metadata intended to spur research into music recommendation / discovery tools.

Calais

Reuter's new Calais API/service provides ontology generation for your docs. They tout it as a tool for the vaulted semantic web. This might be a worthwhile alternative to the simple frequency analysis I've been doing on my iTunes / Flickr mashup tool which presents a slide show of pertinent images from the lyrics of the now playing song.