While the wait continues for Google to release Android Lollipop as an over-the-air software update and post official factory images of the latest operating system version, a number of developers over at XDA-Developers have taken it upon themselves to take the Lollipop source code and create builds for the Nexus 4, 5, 7, 10 and other devices.
The source-built ports of Lollipop for Nexus devices, alongside the Sony Xperia Z, Samsung Galaxy Nexus and Samsung Galaxy S III Mini, are mainly vanilla builds of Android Open Source Project (AOSP) with no Google Apps or any other enhancements. A list of each custom build can be found below with instructions on how to install the ROM within each link.
Keep in mind that installing these unofficial ports of Lollipop on an unsupported Android device requires some technical skill and could cause problems or security issues with your device. I personally recommend holding out for the official release of Android Lollipop, and advise that users who absolutely want to try these builds backup their device and do so at their own risk.