Software-defined networking (SDN) is a red-hot topic in our industry for 2014 and beyond, with VMware being the leading visionary in Gartner's Magic Quadrant for Data Centre Networking.
There are 3 levels of certification on "Network Virtualisation", all based around the NSX product:
VMware Certified Professional - VCP-NV
VMware Certified Implementation Expert - VCIX-NV (think of this as being at VCAP level)
VMware Certified Design Expert - VCDX-NV
Have a look here for the range of NSX training: VMware Education page