I like stamps that are like puzzle pieces, able to form a bigger picture when together.
Do you have such stamps in your country? I’ll start the ball rolling with a few sets.
2015 Stamps issued to commemorate the Botanic Gardens being awarded UNESCO status.
2009 Stamps celebrating 150 years of Botanic Gardens
2013 Our City in a Garden Stamps
2008 Stamps to commemorate Singapore being the first host city of the Youth Olympic Games
1989 stamps, map of Singapore
1986 Stamps to commemorate NTUC’s 25th Anniversary
2004 Stamps showing Chek Jawa’s marine life
EDIT: So these are known as Se-tenant stamps. The more you know!