At TED in 2007, Hans Roslings announced that the UN had agreed to make their data freely available. Previously it was paid only.
Well they have not only followed up with action, they have done it in style.They have just introduced a new website where you can query all the databases. It is features a very nice google style search, with lots of ajaxy goodness to make finding data even easier.You can find it here : http://data.un.org/.
It is early days yet, and all the data is not there, but you can already do some interesting searches. Some rather peculiar ones too. For example, you can find out how many Internet users there were in the world from 1960 to the present. Here is the data for 1960 : Internet Usage in 1960 - 30 years before Al Gore even invented it :-)