Two addons are to be downloaded:

http://wow.curse.com/downloads/wow-addons/details/tidy-plates.aspx
http://wow.curse.com/downloa....es.aspx

When you first log on after downloading, simply press yes and wait for the reload ui.

Immediately afterwards, you can see the results!

Press V to show only enemy nameplates
Press Shift + V to show only friendly nameplates
Press Ctrl + V to show all nameplates
These commands work with the default blizzard nameplates as well.

I recommend this addon greatly, it's very handy!