Ubuntu Networking :: Computer Drags Down Internet Speed ?

Lately my computer, while connected to our router and using the internet, drags the connection speed of everyone in the house down tremendously, to the point of being unusable in many cases. Even buffering a ..... video causes tremendous lag across the network, making second-long load times stretch to a minute or more.

Now, our connection isn't the greatest, but ..... shouldn't cause that much lag, so I'm thinking there's something else at work. Is there some application I could use to monitor what programs on my computer are accessing the internet?