CIA World Factbook: Real facts about every real sovereign state in existence. If an entity claims to be a state but isn't in the CIA World Factbook, then it's almost certainly a micronation.

Flags of the World: Comprehensive and exhaustive vexillological reference site, documenting just about every flag that's ever been flown - including those from a number of notable micronations.

Footnotes to History: A fascinating and detailed exploration of the countries "you didn't learn about in high school" - quirks of history, failed secession attempts and countries that didn't quite make it for one reason or other. A veritable atlas of odd, largely forgotten states.

French Micropatriological Institute: A site exploring the entire spectrum of micronations, ephemeral states and microstates. Published by Fabrice O'Driscoll, the late French academic and former Vice Foreign Minister of the Principality of Hutt River.

Unrecognised States Numismatic Society: US-based, ANA-affiliated group of coin and banknote collectors focusing on micronations, unrecognised states, secessionist groups, historical oddities and related exonumisma.

Unrepresented Nations and Peoples Organization (UNPO): Netherlands-based international organisation representing indigenous peoples, minorities, and unrecognised, occupied or otherwise disputed territories.