Needed: Application to dynamically control my bandwidth!

[PopWeasel]

I run a lot of applications that transfer data over the internet and lately I've been wondering if there's such a thing as an application that will "dynamically control my bandwidth?" By this I mean that I'd be able to manually set how much bandwidth a particular application is allotted. This would give me greater control over transfers and would allow me to place a higher priority on transfers that are more important than others. A tool that could do this for me would be very useful. :P

Any suggestions? TIA.