Of course, there are many weapons that are currently being used in the conflict in Iraq.
Probably the two most common weapons are the M16A2 rifle and the Kalashnikov AK-47 assault rifle.
The M16A2 is the standard rifle that is used by infantry of the United States Army. It has been in use for decades -- since the Vietnam War in the 1960s.
The Kalashnikov AK-47 (and variations made by various countries) is the most widely used weapon among irregular, non-army groups of fighters around the world. It was originally made by the Russians in 1947 and has been widely copied and widely distributed.
I'll only list the weapons used by the US and Insurgents as i am not sure for the rest:
United States of America
M249 SAW (Squad Automatic Weapon)
M240 (Mounted on Humvees)
M2HB (Mounted on Humvees)
M14 DMR (Desinate Marksman Rifle)
MK 12 MOD 0 SPR (Special Purpose Rifle)
M67 Frag grenade (fragmentation)
M18 smoke grenade
AT4 Anti-Tank Weapon
SMAW Anti-Tank Weapon
Javelin Anti-Tank Weapon
Stinger missle Anti-Aircraft Weapon
M203 Grenade Launcher (Mounted below M4s and M16s)
Most weapons used by insurgents are either Russian made or just copies.