JungleBot is a 'Twitter Bot' that allows users to query Amazon.com without leaving the comfort of the Twitter command line. Right now, JungleBot allows users to search for books, DVDs, and music by sending a direct message to JungleBot.
WhoShouldiFollow looks at who your Twitter friends follow to suggest new people. By adjusting the sliders on the results page, you can give greater preference in the ranking to less popular Twitter users, or those who are near you.
The algorithm is an item-to-item collaborative filter, somewhat similar to how Amazon makes recommendations.