Measuring data transfered

Are there any programs out there that can measure how much data I transfer online in a given period?

I'm going somewhere where the internet fee is based on data transfered and I'd like to know what kind of charge I'm in store for.

Thanks!

 

http://www.netlimiter.com/

http://www.netlimiter.com/img/scrshots/nl2shot_stats.png

 

I'd suggest NetMeter. I found it robust and free from spywares, etc. I only used the stable version 1.1.3.
http://www.metal-machine.de/readerror/index.php?page=10

 

I second netmeter. Been using it for years.