I know that Belgium isn't considered to be in the top 10 weapon manufacturers, but FN Herstal (the number one weapon producer in Belgium) did have something to do with a few iconic weapons.
Submachine gun:
FN P90: Originally developped by FN Herstal, now popular all across the globe.
Assault rifle:
SCAR-family: Manufactured by the US, but the design was Belgium made, courtesy of FN Herstal.
FN F2000: Not in use by the US (surprise), but it has made an appearance in a few movies as a "high-tech" assault rifle. In use by Belgium, but also Poland, Slovenia, India, Croatia, ...
FN FAL: Also known as a "battle rifle", this rifle is (has been) used by more than 90+ countries, with more than 2 million units produced. One of the most popular and known NATO weapons, although the US decided to use the M16 instead.
Machine gun:
Minimi (also known as the M249): Considered to be an American weapon, it is actually a Belgian designed and produced in the US by a FN subsidiary, FN Manufacturing LLC.
Non-lethal:
FN 303: A riotgun, utlized in Iraq, Afghanistan and Libya. Used by the US.
A pretty short list in all, I know, but these are the most iconic and well-known weapons. Belgium isn't the biggest weapon manufacturer, but it seems to be pretty innovative when inventing more death-dealing stuff. I don't know just how detailed the weapon descriptions are going to be, but I would love to see a few "made in Belgium" tossed in there.
For more information, you can also view the (english) webpage of FN Herstal
here.