Well, whether you polish or not you always want to wax. I use the term "wax" rather casually here - by "wax" I mean either a traditional carnauba or carnauba blend or one of the more modern synthetic sealants. A sealant will generally last longer but some people think they leave the finish too much like it's wrapped in plastic. Carnauba tends to give the deepest, warmest look.

Having said all that, a proper full treatment would entail washing, clay bar to remove all the bonded surface contaminants, and then a good paint cleaner/polish to remove swirls, light etching, water spots, etc. All of this prepares the surface for the wax or sealant and, if done right, will leave the finish looking gorgeous before you even wax it. Especially black.

I lean heavily to Meguiar's Professional line of finish care products and am a big fan of machine polishing. For the wax/sealant itself, my absolute favorite combination is two coats of Meguiar's M21 Synthetic Sealant followed by a coat of their M26 High Tech Yellow Wax. Just stunning.

Have a look at meguiarsonline.com for more info than you ever thought possible on the subject.