Especially the Open Knowledge Foundation, which has been a pioneer in this field, the Open Rights Group, Access Info, MySociety, and in the US the Sunlight Foundation, Creative Commons and the Electronic Frontier Foundation.
We'd also like to thank the many people in the UK Government Cabinet Office who've helped support open data in the UK (especially former Director of Digital Engagement Andrew Stott), as well as the many dedicated developers and activists in the UK, including Rewired State, who've helped make the UK such a vibrant place for open data.
Finally we'd like to say thanks to the World Bank Institute, who are our partners on the Open Company Data Index and are doing great work on Open Contracting, and also to the World Bank itself, for pushing on open data in a global and development context.
We love OpenSpending, Who's Lobbying, FarmSubsidy.org, OpenlyLocal and OpenCharities, and of course OpenStreetMap. We'd also like to mention Euroalert, Corpwatch API, Public Resource.org, the Internet Archive, and OpenKvK.nl.
ScraperWiki is an awesome tool for getting extracting data from government websites (and is actually used by the UK Government, as well as OpenCorporates). Anyone interested in this area should also check out Tim Berners-Lee's open data Ted Talks, and Carl Malamud's inspiring 10 Rules for Radicals.
OpenCorporates would not be possible without a huge number of open source programs, tools and resources. It's built on the RubyOnRails framework, uses the MySQL and Neo4j databases, on servers running Linux. We also use famfamfam icons and flags, Twitter Bootstrap, and JustVector icons.