I'd consider finding out whats the cause. The only things I can think of.
1, Your internet connection is the cause
2, Your computer is the cause
3, The server is crap ( I've had it happen tons even when even my pings low )
4, Unlikely but everyone who was playing had a bad connection?
1, If you ping is fine on the server ( 100 or less is fine ) you could test the bandwitdh at www.speedtest.net There usually pretty accurate.
2, Download Fraps here
and see how many frames per seond you're getting in game. As long as it's constant and stays above 35 it should be playable.
3, Try different servers and see if you get the same problem.
And for your question. I'll try and name a few.
If you have a wireless router I'd suggest turning off the wireless signal unless you use it. Might be a pesky neighbour stealing your bandwitdh.
Programs such as Xfire, MSN, AIM, Limewire, Azureus, even your anti-virus, ect will use your bandwitdh. Has this problem always been there or has it just occured?
Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.