Japanese variety show Tama New Town says they recently got some information the next entry in the Dragon Quest series, Dragon Quest X. On their next show they will be talking about it. So if their claims are true, keep an eye out.
As of right now, the only details that have been announced about Dragon Quest X is that the title is planned for the Wii.
Dragon Quest IX has yet to hit North America, but is scheduled to be released this Summer. It will probably be awhile till we see Dragon Quest X release in Japan, and probably even longer to see the title released in western markets.