Prestige
Contrary to popular belief, you don't lose everything when you prestige. Here's the purchasable things that you keep (there may be more, and it may have changed as of patch 1.04)
-Emblem icons, layers, and Playercard backgrounds
-Having your clan tag and Emblem on a gun (you still need to get the level to put them on, but they'll be free)
-Different Reticules for sighs (confirmed Red Dot Sight)(doesn't save all of them, the top few ones aren't saved, but the rest are) and reticule colours (not lens though)
Things that are reset are:
-Challenges (except lifetime)
-Purchased Guns, Camos, Lens colours, attatchments
-Face Camos
-Perks, and Pro versions
-Killstreaks
-Equipment
-Lethal Grenades
-Special/Tactical Grenades
Things that are kept(without needing to purchase)
-Your Current Playercard
-Leaderboard and Combat Record scores
-Fileshares
-Available Playlists
If you need more help, we've got more Call of Duty: Black Ops cheats and also check out all of the answers for this game
Comments for this hint