Well, here is just the right tool for monitoring all data in and out of your PC through the internet connection. Best thing about it is that it is open source and all free without any adware or sharewares coming bundled with.
So what is it? It is called BitMeter 2. Some of the features I found very useful are that, it can visually show all data in and out live, as well as historical data based on time, be it hourly or daily and it can be set to alert you when, a certain usage limit is reached. Depending on the service your ISP is providing, you might have a usage limit per month. So, it is a good thing to know exactly when your data usage [total downloads/uploads] limit is going to reach before the month ends and how much data usage is remaining in a very convenient way.
Another good feature is that, it can tell you exactly at what speed your data is being transferred up or down at any given time. It has a built in calculator that can give you the time it will take for you to download a certain amount of data and vice versa. All these information is shown in an intuitive way using graphs. The displays can be customized or configured as well, to suit your needs.
There are many more features that come with it. Just install and set it, and see how much control you have over your internet usage.