So far, 92 countries including the United States have issued travel restrictions for travelers coming from affected areas.
This International Air Transport Association list, which is being monitored and updated daily, is probably the best—and most reliable—list of travel restrictions we've seen out there. Because things are constantly changing, and the fact that we're changing OUR own list every few hours to boot, it may not accurately reflect the latest developments within the last day or so.
(For instance, as of this writing, the entire country of Italy is on lockdown. Even current tourists caught there are being quarantined in their hotel rooms for the time being.)
In most cases, countries will not allow citizens from the most heavily affected nations (South Korea, Italy, Iran, China, Japan in some cases.) to enter, while a select group of countries like Turkmenistan are going full out. For now, residents from 41 countries and principalities won't be allowed to enter the central Asian country.
Good time to adventure at home?