John James Jacoby

This plugin is a library to connect your BuddyPress powered website to the XML or JSON Foursquare API.

BP Foursquare API

An API to connect BuddyPress to Foursquare.

mitchellhislop

This plugin ties into Foursquare’s remote tip/todo functions, which in turn allow a website operator to 
easily embed the buttons. It was developed by <a href="http://mitchellhislop.com" rel="nofollow ugc">Mitchell Hislop</a> of <a href="http://smcpros.com" rel="nofollow ugc">SMCpros</a>

WP-Foursquare Todo Adder

This plugin allows a publisher to easily add a foursquare todo button to a post.

BP Foursquare API vs WP-Foursquare Todo Adder