Search around here. I have seen performance exhaust and lowering by installing the LegacyGT suspension. There is a group buy going on for a lightweight billet aluminum crank pulley over at LegacyGT forums and they are looking for some Outback drivers to help get enough people for the buy. Other than that most people are installing a 19mm rear sway bar. Kartboy makes sway bar drop links, but the are expensive for not much performance gain. There are some polyurethane suspension bushings available too, but they are from overseas so shipping costs 10x the actual parts. I'd like to get poly bushings on my sway bars as I have read this is worth the effort.
Your best bet is to sign up for an account over at the LegacyGT forum and search over there. Those guys have done a lot more with performance mods on the 3.6 and many of the mods (but not all) can be applied to the Outback as many parts are shared.
It would be really nice to have access to the Subaru parts catalog to cross reference part numbers, but I have not found a way to get this on my PC yet. Only the factory service manual which does not include parts.
