You unlock them at level 51. Although I have seen other people get them before I don't know how though.
At level ten you unlock the playercard
It is unlocked at level 69.
In Black Ops multiplayer you unlock the AK-47 at level 38.
you dont unlock it at a level you unlock it by killing somone right before they get a 10 kill strick and you will earn the pot leaf emblem
You unlock gold camo in black ops, when you reach prestige level 14, level 25.
Your are reset to level 1 and have a new emblem next to your name, and you can unlock new titles and emblems
When you rank up to level 35 you will unlock it.
You have to get to level 44 and then pay the $2000 to unlock it
You get to level 50
Level 44
the crossbow i believe
get to the level where you unlock it :):P