Dion Hinchcliffe wrote an excellent summary of 17 products in the mashup tools market (July 2007). He tries to answer the question: "What's typically missing from today's mashup platforms to make them both useful and desirable in the enterprise?"
This URL opens a Google Docs spreadsheet. It loads quickly, is very handy, and gives you a great annotated catalog of all TEDTalks thru March 30, 2009.