3rd party Silverlight controls

ComponentOne
A full suite of components including custom layout panels, menus, treeview, textboxes, charts and more.

DevExpress
A free datagrid with grouping, sorting, resizing, template support, multi-row selection and more.

Infragistics
A large collection of charts and gauges for data visualization.

Intersoft
Two alternative controls to the standard menu, FishEye and CoverFlow.

NETiKA Tech
An implementation of the standard Windows Forms control library, developed as Windows Forms Applications and run as Silverlight applications.

Telerik
A full suite of components including menus, tabcontrols, treeviews, mediaplayer, progressbar and more.

Visifire
A large collection of open source data visualization components.

Xceed
An asynchronous, multiple file upload control with data compression.