I have a VZ SV6 5 Speed Auto and I want to achieve the biggest power gains possible without supercharging. What would you recommend?

These are some products which can increase the power gains. Links are given below:

COLD AIR INTAKE TO SUIT HOLDEN VZ V6 http://www.maceengineering.com.au/epages/shop.sf/en_AU/?ObjectPath=/Shops/mace/Products/CAI609/SubProducts/CAI609

COLD AIR INTAKE MANIFOLD INSULATOR ALLOYTEC VZ-VE http://www.maceengineering.com.au/epages/shop.sf/en_AU/?ObjectPath=/Shops/mace/Products/MI603

25MM COLD AIR INTAKE MANIFOLD INSULATOR ALLOYTEC VZ-VE http://www.maceengineering.com.au/epages/shop.sf/en_AU/?ObjectPath=/Shops/mace/Products/MI631

VZ-VE ALLOYTEC & LLT SIDI V6 BALANCERS http://www.maceengineering.com.au/epages/shop.sf/en_AU/?ObjectPath=/Shops/mace/Products/PB620/SubProducts/PB621

MACE RECALIBRATED ECM TO SUIT VZ-VE ALLOYTECS, CAPTIVA & RODEO ENGINES http://www.maceengineering.com.au/epages/shop.sf/en_AU/?ObjectPath=/Shops/mace/Products/COMP621

HOLDEN VZ-VE ALLOYTEC V6 CAM PACKAGE (Custom tune required) http://www.maceengineering.com.au/epages/shop.sf/en_AU/?ObjectPath=/Shops/mace/Products/CAM616

HOLDEN V6 ALLOYTEC MANIFOLD http://www.maceengineering.com.au/epages/shop.sf/en_AU/?ObjectPath=/Shops/mace/Products/IM609/SubProducts/IM609

Beyond this, you could consider getting the cylinder heads ported, and the engine built such it's able to revved harder (reliably increase rev limit). The later would be handy if you wanted to run even larger cams then the ones we currently have off the shelf.