Just announced at TechEd 2013 North America the Cisco Nexus 1000V Switch for Hyper-V is finally out of beta and available for download!
Title: Nexus 1000v Switch 1.5.1 release for HyperV platform
Release date: 06/03/2013
File size: 177.93 MB
File name: n1000vh-dk18.104.22.168.SM1.5.1.zip
Download URL: Click here to download
Note: This download is intended for Hyper-V in Windows Server 2012, not 2008 or 2008 R2 Hyper-V hosts.
GETTING UP TO SPEED
If you haven’t heard of the Cisco Nexus 1000V before, this is a virtual switch that is inside the Hyper-V host itself, not in Cisco physical hardware.
This page has a good overview: