I see the date picker control in WinRT JavaScript/HTML5. Where is that control for XAML?
Syncfusion's WinRT Studio (Beta) includes a very, very good DatePicker and it's free to use.
http://www.syncfusion.com/products/winrt
The best one I've found (complete with templating and xaml friendly formatting options) is:
https://github.com/jasonmitchell/WinRT-XAML-DatePicker
You can inspect our package of WinRT components. It contains date picker component as well as a lot of other UI components: radial and plain menus, color picker, rating controls and so on. And it's totally free btw ;).
You can find the following control that looks like the same as the javascript one: https://mytoolkit.codeplex.com/SourceControl/changeset/view/25356#181302.
Note that Win 8.1 includes built-in XAML controls for DatePicker, TimePicker. So if you retarget your project to target Win 8.1 you will now get these controls.
retargeting: http://msdn.microsoft.com/en-us/library/windows/apps/dn263114.aspx
There is no date picker control in the standard Windows 8.0 toolbox. However, look at the Callisto for many handy WinRT XAML controls, including the date picker control. https://github.com/timheuer/Callisto