A listing on Amazon France indicates that a new Xbox 360 bundle will be launching on September 15th.
According to the page—my French is a little rusty, mind you—it's the 250GB model of what one would presume to be the redesigned, super-slim Xbox 360, along with Tomb Raider and Halo 4. The bundle is priced at 249 Euros (roughly $325), which could very well be a placeholder, along with the aforementioned September release date.
Bearing in mind the fact that Microsoft has yet to make any official announcement, we've got to treat this as mere conjecture for the time being, though, I expect we'll hear something about holiday Xbox 360 bundles in the (somewhat) near future, hopefully along with a price cut.
Thanks to Jason from PlayStation LifeStyle for the tip!