I think most worldwide (and US) collectors recognize the US airmail postage stamp I’m writing today. In 1980 US post (along with Italian Post) issued a commemorative stamp to honor the 280th anniversary of Philip Mazzei’s birth.
The stamp exists in two different perforations: 11¼ and 10½x11¼ (latter having over 10x catalog value to normal stamp). In addition, this stamp has plenty of (easy-to-find) flyspeck varieties. They are nothing valuable or rare, but enough to catch the eye of casual stamp collector like me.
I also have found a pair where the airplane silhouette has an additional blue shadow caused by so called “kiss print”:
You might also be interested of related posts about Stamps and postal history of USA.