9 May 2014 - IPERF for Windows with User Interface and Charts released. Native Win32 port (not Cygwin) with QoS (DSCP set). Free download of trial version is available.

IPERF is a professional bandwidth test tool for qualifying performance of corporate networks and the Internet. Both versions: interactive graphical and command-line for batch operations are provided. Download Free Trial
Check out the videos below for IPERF Charts with UI and command-line version.

Here are the screenshots of IPERF on WinXP and up:
Win2008 Server: IPERF UDP Server Windows Server 2008: IPERF UDP Client
Windows XP: IPERF UDP Client    Windows 7: IPERF UDP Server    Windows 8: IPERF UDP Client

IPERF Charts in real-time - video

false positive
antivirus alarm?
follow tutorial
I prefer IPERF:
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"I love this IPerfwindows with charts, I am a Senior Network Engineer and I rely on bandwidth measuring tools for VOIP and Data issues every day. I have other such tools but IPerfwindows just makes my life easier, with the real time graphs and easy setup, I can spot problems immediately. With IPerfwindows, I am able to save my reports with ease.
THANK YOU IPerfwindows.com"
Brian Landa

"The program is working very well. I'm testing a DOCSIS 3.0 cable modem in an 8x4 channel bonded mode. I'm able to get ~300Mbps downstream and ~100Mbps upstream without errors."
M. Pulliam
Cisco Systems Inc

"IPERF helped us identify network performance problems by allowing us to test connections between the Windows and Linux servers in our environment."
B. Kingsolver
Land Title

Real-time charting of TCP and UDP tests.

IPERF User Interface - video

UDP and TCP tests in graphical User Interface.

Bandwidth Test with QoS - video

Bandwidth test with QoS set, using command-line version of IPERF for Windows.