I had unlocked my Nexus 7 and everything was great for months. I came home from work and it was stuck in a boot loop. I somehow managed to delete the OS while trying to fix it. I have access to the Team Win Recovery Project v2.2.1 but nothing else. What's the best way to reload the OS?
XDA is the only place to go.
They have plenty of ROMs to choose from, including stock builds for your Nexus if you want timely updates from big G.
You could also try downloading the factory image from Google. There are instructions with how to use it on that site too. This will completely wipe your device including your files.