Right now, there are 22 generic top-level domains (gTLDs), many of which are specialized (i.e. .aero for the air-travel industry, .gov for U.S. government sites, .edu for educational institutions), and many more country specific TLDs that are governed by ICANN (The Internet Corporation for Assigned Names and Numbers).
On Jan 12, 2012, the application process will open up for 3 months, and anyone will be able to bid for a new gTLD of their own specification – within reason. GTLDs that contravene trademarks won’t be allowed (no .burgerking for you, unless you’re Burger King), nor will gTLDs that are confusingly similar to existing gTLDs (so if you were thinking of getting .cmo to catch all of the typo traffic it’s not going to happen).
An interesting article that considers what DotBrand will mean for SEO and reputation management. If you’ve got $185,000 to purchase a desirable gTLD that everybody wants a domain at (For example .xxx) this could be a worthwhile investment.