Worldwide: OpenRailwayMap, The Man in Seat 61
Europe: Trainline, Omio, RailEurope
by Country (Alphabetical)
Argentina: Argentina.gob.ar
Belgium: SNCB
Botswana: Botswana Railways
Bulgaria: BDZ
Canada: Via Rail Canada
China: trains.china.org.cn
Denmark: DSB
Egypt: Egyptian National Railways
Europe-wide: Official Interrail Site | Trainline
Finland: VR
France: SNCF
Germany: Deutsche Bahn
Greece: TrainOSE
Hungary: MAV-START
India: Indian Railways
Italy: Trenitalia
Netherlands: Nederlandse Spoorwegen (NS)
Norway: NSB
Pakistan: Pakistan Railways
Poland: Rozklad
Portugal: Comboios de Portugal
Romania: CFR
Russia: RZD
Switzerland: SBB
South Africa: Shosholoza Meyl, Luxury Blue Train
Spain: Renfe
Sweden: SJ
Turkey: TCDD
United Kingdom: RedspottedHanky | Trainline
United States: AMTRAK
Zimbabwe: NRZ