What's a good, light, unintrusive and free tool to monitor network/internet speed for the Mac?

I need to know how much internet activity is taking place on my iMac. I don't want something very detailed like Little Snitch or some professional network analysis tool. I'm looking at something simple that can simply upload/download speeds in the Mac OS Menu Bar next to the WiFi and other icons.

If you've used DUMeter or NetMeter on Windows, you know what I'm talking about.

Answer

Found the answer from another question. iStat Menus and MenuMeters do what I need.

Thanks to @Sathya!