This is my personal list of banned subdomains for projects that allow customers to choose their own subdomain.
Feel free to contribute to this list! The more the better! Fork and do a pull request with your updates.
Try to separate out lists. I'll further refine my own in the future.
I've added the first of a few other lists, like an always-outdated list of the top 100 of Fortune 500 companies. The idea behind this list is to protect domains that will probably have a specific contract instead of using a signup form and credit card. By protecting these domains, you'll avoid issues where Apple wants to use your webapp but somebody else (possibly malicious) decided to use that domain instead. You'll probably want to use a different denial message with these (such as "This subdomain is reserved. Please contact our sales department for help registering this account.").
I release any data in this repository into the public domain, with the understanding that I take no responsibility for what is done with it, I provide no warranty or guarantee for anything, etc. (See LICENSE.md for legalese copy of the same public-domain release via Unlicense.)