Go into your Steam settings and make sure your connection setting is correct (Steam appears to like to default the setting to a pathetic 256k)
Also make sure your download region is correct.
For Black Ops Multiplayer:
Launch the game and open the in game console by pressing the ` key which is located next to the number 1.
Next apply the following commands:
1) /snaps 30
2) /cl_maxpackets 100
3) /rate 25000
4) /sv_maxrate 25000
This should lower your ping while playing online games.