ProgrammableWeb's API Directory has a list of 62 real time APIs including the most popular: A tie between the Twitter Streaming API and Thrutu API. Real Time APIs can aid developers in producing applications pertaining to monitoring, travel, user verification, search, data validation and more.
Our API directory now includes 134 travel APIs. The newest is the TakeABreak API. The most popular, in terms of mashups, is the Kayak API. We list 12 Kayak mashups. RESTful APIs are the most popular. Below you'll find some more stats from the directory, including the entire list of travel APIs.