First stop, Yalumba.
If you visit the Barossa, do yourself a favour and stop off at Angas Park.
This is one of the few places you can buy Australian dried fruit, and it tastes exactly like I remember. I walked out with delicious dried apricots, peaches and nectarines (which I have been happily munching on since we got back to Cambodia). Tuesday is senior's discount day, so do what we did and bring your parents!
I also spent a lot of time admiring the gum trees, one of the things I love about home.
When we arrived just 10 minutes before closing the new chef and winemakers were preparing the new menu and doing a tasting, so we were fortunate enough to hear all about Saltram's wines from their two winemakers, we felt very privileged. After chatting there til well after closing we headed home with our goodies.
If you are doing the Barossa Valley I would recommend both Yalumba and Saltram (but honestly there is no shortage of good wineries in this area).