The current flag dates back to the middle ages, maybe as far as the 12th century. This makes it not only one of the youngest national flags of the world (since 2004), but also one of the oldest! (Even if it has been in disuse for most of its history.)...
Not sure if Coat or Arms are allowed but I really love the design. Vestland in Norway is famous for the fjords and I think the design captures this really well.
I found the flag on Wikipedia, but I cannot find any reliable sources verifying that it is actually used or officially adopted by somebody. So take it with a pinch of salt....
The provinces of Sweden are historical and cultural regions. Today, they no longer have any administrative function, but still serve as a basis of cultural identification....
The AK-47 and hoe of the Mozambican flag can also be seen as a version of the hammer and sickle, else the symbol is no longer used on national flags today....
(Since you almost need a magnifying glass to see the small purple fields in the rainbows of the flags of El Salvador and Nicaragua, I think they barely count.)...