Various countries have released or will release Trek-themed stamps.
The stamps include Klingon ones, as well as stamps featuring the original series, The Next Generation, and Star Trek: Enterprise.
From Antigua and Barbuda come A Very Klingon Christmas. This rather unique release features artwork by Patrick Faricy and the stamps come as two miniature sheets.
From The Gambia comes a multi-stamp sheet featuring the crew from Star Trek: Enterprise.
Grenada Carriacou and Martinique have released stamp sheets featuring the crew from The Next Generation. Captain Jean-Luc Picard gets his own special stamp in this release.
Finally, Grenada has released two stamp sheets featuring Spock. One of the sheets shows the character in various scenes from original series episodes.
Source: The Trek Collective