As I get myself ready to move my Winform applications to XAML, I was wondering what are the must-have third party XAML controls that will save me developing time and will make my app look shiny with little work? Thanks, Nestor
XAML is markup language rather than a platform. In fact, you don't even have to use XAML to write WPF applications if you really don't want to. Since you're talking about converting from WinForms I believe that the question you're asking is more one of which third-party WPF control kits exist, so I'll answer on that assumption.
There are a few companies that have pretty extensive suites. As Shoban mentioned above, Telerik is one. You also have Infragistics, Actipro, Component One, to name just a few.
There are also quite a few specialty libraries to aid in Business Intelligence, Graphics Processing and more.
In other words, it's not possibility to make a good recommendation as to specific control libraries, but I can point you in a couple of directions.
WindowsClient.Net attempts to maintain a control gallery (not just for WPF, either). That's a good place to start. There are also software sales companies such as ComponentSource which can also set you in a direction or two.
I tried to link the other companies, but SO apparently thinks I'm too much of a noob to be trusted with high-security stuff such as multiple hyperlinks. :)