I’m very fond of one of our newest products www.silverlightmigration.com 
It provides a way to refresh your applications to take full advantage of XAML,
solves deployment issues, runs in Windows, Mac OSX and in some Linux with
MoonLight
And we are event tuning it up for the next jump: Windows 8… keep tuned for that.
One of the things a like most about this solution is XAML theming.
In general there are good themes but today I would like to recommend the SystemColors theme
from http://blogs.msdn.com/b/corrinab/archive/2010/04/12/9994045.aspx
You can download it from here.
This theme allows you to style all core, sdk and toolkit controls so they will use the theme that
you currently have in Windows. These might be very useful for some LOB applications,
so the applications can see more like native applications, and with the advent of Silverlight 5 and more
native integration, better Out-of-Browser execution I think it is just fine.
See some screen shots:
