Free network performance testing utility?

Hello Guru's,

I am looking for a free utility I can use to test network performance, such as throughput etc..

Looking for free because it will mostly be a one time useage.

Thanks,
Eisen

QCheck is fine, but a little short and opaque for my liking.

I'll suggest iperf.

E.g.

server: iperf -s
client: iperf -c server -l 64K -t 12 -i 3 -r

-l 64k: send 64k of data at a time (same as Windows typically)
-t 12: run for 12 seconds
-i 3: report performance every 3 seconds
-r: transmit to server, then reverse direction