How do I monitor what is being uploaded and downloaded

I have a very expensive internet connection and pay for every bite I upload and download. While in idle it seems like I download and upload quite a bit. I have gone in and try to kill processes that I think is causing this, but this is quite a task. Is there a recommended tool out there that will help me to track the culprits in all the up-and downloading?

Some browsers pre-fetch pages, make sure it is turned off.

Some firewalls have a monitoring functions. As well as some newer High end Routers.

MS is one for its Advantage Plan. Make sure your pc's are free of Adware and Spyware. Generally it takes at least 2 different programs/scanners to cover all the basis.

Yea Good Old Fashion "PULL THE PLUG" Works every time.

A Sniffer??

WireShark will tell you anything you need to know, but the learning curve is kinda high. AnalogX has some free utilities that do what you need I think.

If you have a router, you could just get rid of the default rule that allows any traffic from your PC to go out to the Internet. Instead, create rules that allow what you actually use (like http, ftp, smtp, etc). This will prevent other applications such as spyware from being able to connect. You would be surprised just how happily many users can exist with only these three ports open.

I couldn't say whether they do or don't. The highly commercialized $50 routers are great for NAT, but once you try to do much beyond that then they aren't as useful.

Using some sort of utility to see what's doing what is probably the first step to take. Then using that information you can selectively lock things down as needed.