The following weapons and equipment can be unlocked by attaining the (multiplayer) levels below:
Assault Rifles
FAMAS - Lvl. 1
M4A1 Carbine - Lvl. 4
SCAR-H - Lvl. 8
TAR-21 - Lvl. 20
FAL - Lvl. 28
M16A4 - Lvl. 40
ACR - Lvl. 48
F2000 - Lvl. 60
AK-47 - Lvl. 70
M14 EBR - Campaign Only
G3 - Campaign Only
Submachine Guns
UMP .45 - Lvl. 1
MP5k - Lvl. 4
Vector - Lvl. 12
P90 - Lvl. 24
Mini Uzi - Lvl. 44
Light Machine Guns
L86 LSW - Lvl. 1
RPD - Lvl. 4
MG4 - Lvl. 16
AUG HBAR - Lvl. 32
M240 - Lvl. 52
Sniper Rifles
CheyTac Intervention - Lvl. 1
Barrett .50 Cal (AKA M107) - Lvl. 4
WA2000 - Lvl. 36
M21 EBR - Lvl. 56
Dragunov - Campaign Only
Secondary Weapons
PP-2000 - Machine Pistols Lvl. 1
Glock 18 - Lvl. 22
M93 Raffica - Lvl. 38
TMP - Lvl. 58
Shotguns
SPAS-12 - Lvl. 1
AA-12 - Lvl. 12
Striker - Lvl. 34
Ranger - Lvl. 42
M1014 - Lvl. 54
Winchester 1887 - Lvl. 67
W1200 - Campaign Only
Handguns
USP .45 - Handguns Lvl. 1
.44 Magnum aka Colt Anaconda - Lvl. 26
M9 - Lvl. 46
Desert Eagle - Lvl. 62
M1911 - Campaign Only
Launchers
AT4-HS - Lvl. 1
Thumper x2 aka M79 grenade launcher - Lvl. 14
Stinger - Lvl. 30
Javelin - Lvl. 50
RPG-7 x2 - Lvl. 65
Other
Frag Grenade - Lvl. 1
Semtex - Lvl. 1
Throwing Knife - Lvl. 7
Tactical Insertion - Lvl. 11
Blast Shield - Lvl. 19
Claymores - Lvl. 31
C4 - Lvl. 43
Knife
Ice Picks
Smoke grenade
Stun grenade
Attachments
Red Dot Sight
EOTech Holographic Weapon Sight
MARS Sight
ACOG Sight (and various telescopic sights that are specific to certain guns)
Thermal Scope
Suppressor
Grenade Launcher
Heartbeat Sensor
Shotgun
Extended Magazine
Full Metal Jacket ammunition (replacement for Deep Impact)
Sniper Scope (will not take up an attachment slot, just like in Call of Duty 4)
Akimbo
Rapid Fire (replacement for Double Tap)
Foregrip
Tactical Knife