I will add a little to Georges excellent answer. If you wnat to Maintain i-TTL flash control using the Radio Poppers system, you will have to add an SB-700, SB-800, SB-900 or SU-800 to your kit to act as Commander.
Only the Nikon version of the Pocket Wizard: Mini-TT1 and Flex-TT5 provide RF wireless i-TTL flash control with Nikon Speedlights. The Mini-TT1 or Flex-TT5 can be mounted in the cameras hotshoe to relay the signal to any number of remote Speedlights, each attached to a Flex-TT5 Tranceiver.
The Pocket Wizard Plus and Multi Max units can only be used in Manual flash mode.
If you don't mind using Manual flash (Manual exposure mode), there are several less expensive options from the Cactus brand triggers available on e-bay to the Paul Buff CyberCync system. Good Luck and Enjoy your Nikons!