Various themes
Colnect (multiple languages) – Thematic search (various references)
Freestampcatalogue (English/German/French/Spanish/Dutch) – Thematic search (with reference to Michel/Scott/SG/Yvert)
phildom philately (English/Spanish) – Domfil Philately. Lots of thematic catagories with Scott and Yvert numbers. For online catalogue a buy in the shop is required
Neofila (English) – Birds, Cats, Flora and WWF
Aircraft/Airplanes
Michel (German) – Michel Flugzeuge – Ganze Welt
Stanley Gibbons (English) – Collect – Aircraft on Stamps
Animals
Animals on Stamps (English) – database with over 65,000 records
Anti-Smoking
Anti-Smoking Stamps (English)
Astro
Astro Space Society (English)
Weebau (English) – Online catalogue of astro stamps (no images), including catalogue numbers of all major catalogue publishers
Bears
Bearstamps (English) – including catalogue numbers of all major catalogue publishers
Beetles
Beetles on Stamp (English/French)
Bicycles
Bicycle Philately – Complete list of bicycles on stamps worldwide. With Yvert catalogue numbers
Birds
Michel (German)- Michel Vögel Europa
Birds of the World on Postage Stamps (English) – All birds on stamps per country. No reference details
Europas fugle (Danish) – Printed catalogue
Maudoc (Italian/English) – Stamps of Italian area featuring birds
Theme Birds on stamps (English) – Complete list of birdstamps worldwide, including catalogue numbers of all major catalogue publishers
Butterfly
Michel (German) – Michel Schmetterlinge (Butterflies) – Whole World
Cars
Michel (German) – Michel Automobile (Cars) – Whole World
Stanley Gibbons (English) – Stanley Gibbons Collect Motor Vehicles on Stamps
Cats
Michel Cats (German) – Michel Hauskatzen – Ganze Welt
CAT a Logo (Italian) – Cats on stamps with Yvert catalogue numbers
Cats on Stamps (English) – Cats on stamps with Yvert and Michel catalogue numbers
Chess
Chess on Stamps (English) – Chess on stamps worldwide compete till 1990, including catalogue numbers of all major catalogue publishers
Christmas
Michel (German) – Michel Weihnachten (Christmas) – Whole World
Cricket
Nazim’s Cricket Page (English)
Countries
LituanicaOnStamps (English/Lithuanian) – Lithuania on World Postage Stamps
Detective Fiction
Detective Fiction on Stamps (English) – Worldwide stamps, with catalogue numbers of all major catalogue publishers
Dogs
Michel Dogs (German) – Michel Haushunde (Dogs) – Whole Wolrd
Ducks
The Federal Duck Stamp Program (English) – Ducks on US stamps with detailed information
Entomology
Entomophila (English/French) – Worldwide stamps, with Scott and Yvert catalogue numbers
Europe
Michel (German) – Michel CEPT Katalog
iBolli (Italian) – all European stamps
Fairy tales
Hans Christian Andersen (English) – with catalogue numbers of all major catalogue publishers
Fauna
Fauna Stamps (English/Russian)
Fish
Exotic Fish (German)
Michel (German) – Michel Fische – Ganze Welt 2017
Football / Soccer
Michel – Fussball – Ganze Welt
Giant Panda
Giant Panda Stamps (English) – with Scott catalogue number
Golf
Golf on Stamps (English/French) – including catalogue numbers of all major catalogue publishers
Holography
Holography and Philately (English) – Book about postage Stamps with Holograms
Horses
Horse on Stamps (English/Russian) – Horses on stamps
Michel (German) – Michel Pferde (Horses) – Whole World
Lighthouses
Lighthouses on Stamps (English) – Lighthouses on stamps worldwide
Michel (German) – Michel Leuchttürme (Lighthouses) – Whole World
Machin
Great Brittain Machin (English) – Not a real catalogue, but with lots of information and album pages
Machin Stamps (English) – The Connoisseur Catalogue of Machin Stamps and Decimal Definitives
Mathematicians
Mathematical Stamp Collecting (English)
Mathematicians on Stamps (English)
Meteorites
Meteorites on stamps (English) – with Scott catalogue numbers
Metro/Underground
MetroPhila (German) – Metro on stamps. Now Germany, started with Europe and Worldwide will follow in the future
Money
Coins on Stamps (English/German/Hungarian) – Money on stamps collection, with catalogue numbers
Motor Vehicles
Stanley Gibbons (English) – Collect Motor Vehicles on Stamps
Mushrooms
Michel (German) -Pilze – Ganze Welt 2018
Olympics
Michel (German) – Olympische Spiele – Ganze Welt 2016
Olympic Stamps Catalogue (English/Spanish) – Online and Published stamp catalogue
Paintings
Arago (English) – American Art on Postage Stamps (Smithsonian National Postal Museum)
Art on Stamps (English/German/French/Romanian)
Hundertwasser Stamps (English) – Very nice site on the painter Hundertwasser
The Stamp Gallery of Czech and Slovak Graphic Art (German/English)
Paleontology
Michel (German) – Dinos – Whole World
Dinosaurs on stamps (English) – with Scott reference
Paleophilatelie (English) – Very extensive overview of stamp related to paleontology
The Illustrated Catalogue of Dinosaur Stamps (English)
People
Ghandi (English) – Ghandistamps with stamp about Ghandi worldwide
Jules Verne (English) – Jules Verne Stamps
Plants
Plants on Post Stamps (Russian/English)
Roses on Postage Stamps (English) – including catalogue numbers of all major catalogue publishers
Red Cross
Michel German) – Michel Rotes Kreuz – Ganze Welt
Reptiles
Reptile Stamps (English) – with Michel catalogue numbers
Scouting
Michel (German) – Michel Pfadfinder – Ganze Welt
Ships
Michel (German) – Michel Schiffe – Ganze Welt
My Watercraft Philately (English)
Turtles and Tortoises
Donald N. Riemer (English) – A worldwide list of turtles and tortoises on stamps (including Scott reference)
Unusual
Dentelli Stravaganti (Italian/English) – Unusual and unconventional stamps all around the world
Volcano and Mountains
Mountain Stamp (English) – Volcanoes and mountains on stamps worldwide
WWF
Michel (German) – Michel World Wide Fund for Nature
WWF Stamp Catalogue (English/Russian) – WWF stamps since 1987