Limiting Network Bandwidth to the Internet

I am trying to figure out how I can manage the amount of Internet Bandwidth each user on my network can use.
I know that I can limit the bandwidth of the ports on a switch, but that would also limit the local, LAN bandwidth available to that workstation. I want them to be able to transfer data over the LAN at full speed, I only want to limit their connection speed to the internet.

Any ideas?