What is best tool to measure network latency?
Solution 1:
You could try tcping to measure latency to port 80 of the sharepoint server.
tcping.exe is a small console application that operates similarly to 'ping', however it works over a tcp port.
Solution 2:
I suspect you're not really interested in ICMP latency. These waterfall graphs are probably better for diagnosing where your sharepoint setup is ailing.
In general for public facing: http://www.webpagetest.org/
With FF: http://www.getfirebug.com
With IE: http://www.httpwatch.com/