Network Performance Testing?

ItsMr.Data asks: "Recently, the department I work in has been planning on rolling out a new gigabit backbone network. We have been looking for ways to test network congestion. I am looking for a simple but accurate tool to test different paths through the network. I looked at Iperf, but I wonder what other test setups are out there, and if any are customizable to emulate differing types of traffic, such as streaming media, file sharing traffic, and video conferencing. So, what network performance testing setups do you use?"