At Big Cat Rescue all of our staff, volunteers and interns stay in constant contact with each other by two way radio while on the sanctuary grounds.
We use Motorola because of the low price.
We currently order them through http://www.bhphotovideo.com/ but are always looking for a better deal.
We have tried many different models and recommend this one http://www.bhphotovideo.com/c/product/685350-REG/Motorola_MC220R_MC220R_Talkabout_2_Way_Communication.html.
It is sturdy and relatively reliable. The newer models claim to have a wider range, but fail to preform any better than this one and cost significantly more.
We also recommend staying away from the AAA battery options, as they suck batteries up like crazy.