I've just released the first version of LANBench here - http://www.zachsaw.com/?pg=lanbench_tcp_network_benchmark
Created it very quickly recently to find the maximum bandwidth of my gigabit switch / NICs in my LAN. LANBench mainly tests your network bandwith, but also to a certain extent gives you an idea of how much CPU is being spent in just transferring data back and forth between your machines.
LANBench takes the HDD subsystem out of the equation and lets you test the raw speed of your network.
Head over and check it out for more info.