What type of storm cloud is this? We have had (and are still experiencing) waves of storms passing through this area of the central Queensland 'Capricornia' coast, Australia.  This area is a subtropical coastal environment, close to sea level.

The following picture is one I took from my the balcony outside my lab (facing east):



The storm was moving to the north (left) and that part of the sky was a featureless heavy cloud. The conditions were as follows:

Ambient temperature: 30C (86F)

Wind: strong, to the north

Conditions: Heavy rain periods, heavy thunder and lightning, about 10 minutes later, the sky cleared, temperature rose and the wind dropped to barely a breeze.  Numerous cloud-to-ground and cloud-to-cloud lightning was noticed from this cloud formation.

I am leaning towards this being a 'scud cloud', but a local weather-enthusiast claims it was a weakly formed non-rotating wall cloud.

What type of cloud is this?
I had a rather difficult time telling how the rest of the cloud structure looks; however, I would tend to believe your weather-enthusiast friend might be correct.

A wall cloud - rotating or not - can also be known as a pedestal cloud and is made up of cumulonimbus clouds; generally forming in the strongest part of the storm.
From what I can tell in the picture and judging by the weather that came from it; it sounds like it was a non-rotating wall cloud. Here is an additional reference page that may help you identify it.