Hi Lars Johansen,
Our landmark Q3 2009 release introduced a bunch of new and updated controls. That is why, we will make sure that our portfolio is stable enough, and reflect all requirements of our clients. Moreover, we have not planned a ListBox control in our roadmap, since it is a core one and should be as basic as possible. If you have any specific requirements on your project that cannot be achieved using RadControls for Silverlight, feel free to share your scenario with us, so we can evaluate it further and help you make most of our toolkit.
Thank you for contacting us, and feel free to contact us further.
All the best,
the Telerik team