testing network cables

I am often faced with trying to work out where network cables come out. For example I find the messy patch panels and have to trace the cat 5 or 6 cables around the patch panel and switch cabinets or across buildings. I need a tool where I can send a tone down a cable then roam around where I think the cable comes out and use a device to find the tone being sent over the cable (without plugging the device into hundreds of cat cables). Can anyone tell me a hardware tool that would do this and the link to the sales web site? AND pls tell me some web sites where there are commands I can use to test whether cables are working? Thanks