For a $50,000 application fee, another half milllion or so in the bank, and the right partners to run the registry, anyone can propose a new TLD to ICANN. That's how Neulevel and Affilias did it.
Other than that, you could start a new country and apply for a ccTLD.
There's another company out there now selling any TLD you want. Only trouble is...they don't work.