Foursquare Connect App

It sounds like Facebook Connect App, however it is not much like Facebook connect.

Read about this from their engineering blog post, and their App Platform documentation to request a preview.

Factual, 1 API for 55 million places

Factual API is another big data API for querying places. It even includes countries such as China.

However, it is currently under Beta so not everyone gets access.

InfoChimps + Geo Data

InfoChimps is a great API provider, with lots of data.

They have recently announced a huge API release with Geo Data. 

They is a pretty exciting release. Now, with an API request, you can get Wiki articles, Foursquare places, weather, etc, of a particular place!