With the latest update, we introduced a PopupManager that handles Z-Index on all popups (RadWindow, RadWindows with TopMost=true, and RadPopup - used in combobox, menuitem, datepicker, timepicker).
The PopupManager exposes four zones: Window, TopWindow, Popup and DockWindow (for future use).
If you want your popup (not RadPopup) to show on top you can set its Child Z-Index to be bigger then 300,000 (this is the starting Z-Index for Popup zone).
I recommend that you use Popup control instead of RadPopup because RadPopup used to be a workaround for a bug in the Silverlight 2 platform and we might drop it from the future versions.
As for the ContextMenu - we will most probably have it for the Q3 release.
We apologize for any inconvenience we might have caused you.
If you have other questions, drop us a line.
the Telerik team
Check out Telerik Trainer
, the state of the art learning tool for Telerik products.