It's not here, but this is a great place to start:
Most of us are lowered on some sort of Legacy specific suspension with sway bars (Legacy GT sways fit the OB).
Anything for a Legacy GT will fit on an Outback (you just lose the ride height, wheels might rub if you go low enough)
SublimeJoe's is a great thread to see what you can do and read through his thought process for the changes he made.
Those two threads will give you a good over view of what can be done. But really it's up to your goals:
Keep outback ride height / slightly better handling - replace struts with KYB (it's an option in the first link) and Rear Sway bar.
Improve handling all around: shocks/springs - Outback specific coilovers (BC/BR - scooby2.5 has them), Legacy GT take off suspension, Legacy Bilstein suspension, Koni, etc. Sway bars - get a rear one and the avo reinforcement bracket. The car feels so much better.