Here's a list of confirmed weapons so far in the upcoming game MW3.
Skorpion (with black furniture)
MP5A4 (full size MP5, with front rails)
SCAR-L (in black)
MP412 (Russian .357 revolver)
Remington RSASS (A JP Rifles based sniper rifle)
Model 1887 (With black furniture, and M1014 style sights)
Remington ACR (in tan)
AK47 (Looks like MW2's with black furniture)
M82 Barrett .50 Cal (Seems to be a MW staple)
Armsel Striker (The infamous MW2 shotgun)
M320 (Portable grenade launcher, Thumper replacement?)
AA12 (has some rails n' junk thrown on it)
Kel-Tec KSG (Or something. Bullpup pump action shotgun.)
The one and only M4A1 (EOTech and magnifier, as well as a Magpul CTR Stock)
Magpul FPG (Probably a G18 replacement)
FN FAL (Looks like the MW2 one with the long mag)
Short Barrel AK Variant (AKS74u?)
So there you have it. Some returning favorites, some newcomers.
Link to Kotaku article with pics: http://kotaku.com/5801353/modern-warfare-3-multiplayer-features-battles-in-brooklyn-clash-in-mogadishu/gallery/ It also contains a list of new multiplayer maps, and multiplayer skins. Enjoy!