Document Classification: We helped Scribd, an online publisher, classify documents.Link (via Data Mining)
Sentiment: We labeled sentiment (buy/hold/sell) for stocks from posts on message boards.
Price Extraction: We extracted prices from popular shopping sites, as well as an open question to find the lowest price on a given product.
Search Relevance: We judged the relevance of a webpage for a search query.
See also: Mechanical Turked color names