In addition to the H6 models, I believe the Outback XT (turbo) models started offering VDC in 06 or 07, as did one of the Forester XT models. Tribeca has it too. To be honest, I think Subaru should offer VDC on all models at this point -- many other brands (Honda for instance) offer stability control across the entire lineup, and the technology is no longer new/novel or expensive. I think stability control is even more beneficial on AWD cars, as it helps keep the driver out of trouble in the marginal conditions that AWD drivers are more likely to be out in. Subaru is somewhat conspicuous in their limited offering of VDC.
I agree with Phil, the 05+ 2.5 H4 models are the sweet spot. Unless you have the need for power, or carrying a lot of passengers/cargo/towing in the mountains, there is no real need for the H6 or H4-turbo models. I will say that in mountain driving with a car full of people and gear, the H4 models do feel a little weak though. I later owned H6 and H4-turbo Outbacks, and they were significantly more drivable in those conditions. The downside is that you lose 4-8 MPG on the highway back in the flatlands. It's always a trade.
Another plus of the 05+ H6 and H4-turbo is that you step up to the significantly better 5-spd auto transmission. This is another option Subaru needs to offer across the whole lineup. The 4EAT is a big long in the tooth, and again, other companies offer 5-spd (or better) across their whole lineup nowadays.