Add new control to the suite: Shuttle control.

Shuttle controls is a couple of ListBox controls and several buttons in between, that move items from one ListBox to another and vice versa. 

Here is an example of the interface:
http://www.mathworks.com/access/helpdesk/help/toolbox/comm/ug/shuttle1.png

Check the following two examples showing how Shuttle control can be easily created using RadListBox or RadTreeView control:
https://github.com/telerik/xaml-sdk/tree/master/ListBox/ShuttleControl
https://github.com/telerik/xaml-sdk/tree/master/TreeView/ShuttleControl

Create an Office2010 theme.

New TimeLine control featuring ZoomBar.

A component to easily chat with visitors on a website.  It's becoming popular to be able to interact and offer support that way.  Maybe based on the Windows Live Components or something along those lines.

I'd like to put in my request to have a control that would allow to magnify a part of the image as mouse goes over. Here is link to see a running sample:
http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=11439
As you move your mouse over, another window opens up to show a magnified version.

Add new control to the suite: Wizard control.

A data form control that allows the users to rearrange the fields using drag-drop and then save the layout. This control would be used in information systems where the admin users should be able to create custom forms for the regular users.

LayoutControl is now officially available since R3 2016 Release.

Develop  a new control - Fisheye Panel.

New Control: WPF Web Browser

A useful new control would be : RadWebcam

It would show webcam view in realtime and call a function each x seconds (or ms), would be useful for :
 - user picture to attach to its user account
 - quick product picture
 - and for my need : call an external function for barcode recognization

I think it would be easy and fast to create this control for WPF, and it would fit perfectly with Silverlight 4 (or 5 ?) webcam support.