It was a little behind the 2014 Nexus devices, but the venerable Nexus 5 is getting its update to Android 5.0.1 today. Along with that, there's a full factory image so you can flash your beloved 5-inch Nexus back to stock. Joy.

2014-12-15 17_04_11-Factory Images for Nexus Devices - Android — Google Developers

The new build of Android 5.0.1 (build LRX22C) can be flashed on your bootloader unlocked Nexus 5. Anything you have on it will be wiped out, or you can edit the script file to remove the wipe command. The full wipe is necessary if you're on some bizarro ROM and want to get back to stock.

Along with the images, there are updated binaries for the Nexus 5 that contain the proprietary drivers for all the hardware. This is of more interest to developers than people who just want to flash stock software, but it's there if you need it.

[Nexus Factory Images, Nexus Binaries]