Application Specific Bandwidth Management?

Is there any utility out there that would allow one to manage bandwidth on an application by application basis?

I have never understood why this is not built into all applications that are network intensive (specially Internet) related. Many applications such as download managers, bittorrent clients, etc. allow you to do this, but the most common applications such as Safari (or any other flavor browser) and iTunes, do not allow for this.

I use download managers when doing large amounts of downloads, so at least I can “tame” Safari or Firefox and bypass this issue when clicking on downloads while browsing. Unless I am in a hurry, I set the download manager to never exceed 50% of my total bandwidth. But iTunes is one of the worst offenders that I deal with. I like to have iTunes set to automatically download updates to podcasts, etc. A lot of times I forget about this, and I launch iTunes for many different reasons to just listen to music for example, and don't realize that it has started downloading in the background, and I am wondering why my browsing has come to a grinding halt. Yes, I understand that I could/should turn automatic downloads off, but that is not “fixing” this problem (and yes, I do no allow simultaneous downloads).

So I am wondering if there is a way to manage bandwidth on an application specific basis. It would be great to be able to allocate certain bandwidth to any network intensive application, and thus be able to have them all running at the same time without any one of them hogging the bandwidth.

I thought there may be a way to do this based on protocol, but that seems very clunky.

Any ideas?