As ScottGu announced in the Mix08 keynote today, we now have a full, rich set of controls built in to Silverlight 2. 

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Kathy Kam recently created a very cool control viewer to show off all the great built in controls.  

Oh, and don't forget about the really rich set of controls produced by our eco-system.  Just a couple of examples:

Nov '08:  Updated the link to the RTM version of the samples page: http://silverlight.net/samples/sl2/silverlightcontrols/run/default.html
Also, be sure to check out the Silverlight Control Toolkit: http://www.codeplex.com/Silverlight/