hi Scott, there are current discussion about renderings if you look a bit around in the last topics. to give you a quick overview for mac its a little more limited but not much.
On the paid recommendations is Maxwell pretty on top because of its realistic and fast renderings also taking its relative low price into account. similar would be Indigo which costs a little less but has pretty much the same abilities. here a current discussion where you will find some info.
of course this can be topped by software which costs quite a heap more but can also do a lot like cinema4d which is very often used for architectural renderings.
blender would be a free alternative with similar abilities in most of the fields.
generally its quite a big topic, so i will not even start with tutorials now if you have not decided on a render setup yet. just be informed that a current development is taking place, the internal render will be exchanged bringing cycles into rhino making renderings for visualisations hopefully feasible. cycles by the way is also a standard render for blender and @nathanletwory is involved in its implementation.