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