In designing a new WPF application I've noticed that the default theme looks somewhat unpolished and unattractive. I've then tried to find a free, well-designed and complete theme but nothing seems to fit.

So could it be that only commercial themes for WPF are really well-designed and there is no suitable free alternative to make WPF apps look great out of the box?

That said, if the answer is "yes", then what commercial and really polished and clean WPF theme would you recommend? Preference is VS 2012 dark theme (light is okay too) or Metro style or Expression Blend style.