This chassis brace from Cusco installs under the car to improve stiffness between the sway bar mounts at the rear. Very lightweight, strong tubular steel design, with a gorgeous metallic blue finish. Besides stiffening the chassis, this bar also allows the installation of the 2006-2007 STi (you'll also need some  to make that happen).

This bar bolts in place underneath your existing sway bar brackets. Fits 2002-2007 WRX and STI, and 2003-2008 Forester. May not fit with aftermarket sway bar brackets.