According to Wikipedia, Regions where you enter once and travel without any further border controls:
- Schengen (26 European states)
- Common Travel Area (UK and Ireland)
- CA4 (El Salvador, Guatemala, Honduras, Nicaragua) for non-air travel
- Nordic Passport Union (Sweden, Finland, Iceland, Norway, Denmark), now encompassed by Schengen
- Island of Saint Martin (France, Netherlands)
Schemes where a special visa is valid for multiple countries
Schemes that no longer exist
- Benelux (Belgium, Luxembourg, Netherlands), expanded into Schengen
- CARICOM Special Visa (15 Caribbean countries), coincided with 2007 cricket world cup