For xfwm4: a modified, somewhat smoother version of the Mac OS Platinum window decorations.
The first screenshot shows the Classico GTK theme and the close, maximize and shade buttons; the second shows the NOX GTK theme and all six possible titlebar buttons.

Unlike PlatiPlus, this xfwm4 theme will pick up on your GTK colors.

A version called SacramentoInset, where the titlebar ridges look like theyre going inwards instead of outwards, is included with the download. You can also download (separately) a version with titlebars that are 4px taller (Sacramento26).