More often than not, comics-themed stamp designers take the easy road. They pick a more or less representative (and hopefully stand-alone) piece of artwork (or have one commissioned) and slap that on a stamp. Much rarer are the stamps that actually reflect the narrative nature of comics.
The best example in my opinion (although contenders are hot on its heels – see below) is this Swiss issue from 1992 by Cosey and printed by then world-leader Hélio-Courvoisier. It was part of a series of three celebrating Swiss cartoonists (along with Zep and Aloys), but only Cosey was able to call up the atmosphere of his Jonathan comics, with their pensive scenes and suggested meanings. And it’s got snowy mountains on it, which is quite fitting for a Swiss stamp.
For a while the Philippines showcased local cartoonists on their annual National Stamp Collecting Month series. The 2003 issue from the short-lived series included a sheetlet which is one of the very rare stamps to actually use a complete, self-contained newspaper strip, in this case the classic Hugo the Sidewalk Vendor by Roddy Ragodon.
From 2009 until 2011 Greenland issued three stamps celebrating national comics, each as a sheetlet, with actual comic art contained on the stamp itself.  The final one, in 2011, reprinted a fragment from Kaassassuk the Orphan. This graphic novel by  Christian Fleischer Rex retold the classic tale of the orphan who was banished from his village but was helped by friendly spirits in nature.
Finally, an issue from the Netherlands by one of my all time favourite cartoonists and designers, Joost Swarte. In 1984 Swarte was asked to design that year’s edition of the long-running Children’s Stamp issue. He was only able to design stamps, no sheetlets or other special editions. Still, he managed to at least suggest a complete story by designing the stamps as if they had been cut from existing comics, with bits from surrounding panels included. Beautiful work, and the custom lettering only makes it more wonderful.
Next time : cartoonists design!