King Springs makes a heavy duty spring with a mild lift. Primitive Rally sold them to me, as well as a subframe spacer kit to help with rear suspension alignment if you lift the car.
KYB makes a slightly stiffer damped shock. I bought mine from circuitmotorsports.net
There are 2 intakes I have seen, Injen (http://www.subaruoutback.org/forums/...ir-intake.html
) and one other... forgot who makes it, oops.
GR STI (2008+) rear sway bars fit.
There are numerous wheel and tire combos.
Rally Innovation and Primitive Rally make lightbars for the front. I have the PR
one on mine.
Primitive Rally makes excellent skidplates. I have those as well.
You should be able to upgrade brake lines. I have yet to cook the fluid in mine, so... not going to bother any time soon.
There is not the huge aftermarket you'll find for the WRX, but there's stuff out there.