Will this do? It's simple... really simple. There are 3 commands doing the same, so pick the one you like most:
/pingpong
/pingcheck
/ping
Then you type "/ping" for example to ping the party or raid.
You can type "/ping guild" to specifically ping the guild.
Also you can "/ping Vlad" to specifically ping "Vlad" for his ping.
The results are returned after 5 seconds, listing all the people that responded and their ping -excluding your own latency, so the results should be accurate, more or less.
*Edit* Updated and corrected a major flaw, thanks SDPhantom for pointing that one out!
http://www.wowinterface.com/download...encycheck.html