There are several ways of producing a single customized map from OpenStreetMap data, depending on which platform you want to use, the amount of customization you need, and your skill level:
If you are happy with the standard map renderings, and don't need to add much extra information, just use the exporter at openstreetmap.org. This doesn't involve setting up any extra software, can be used from any computer, and requires little technical skill.
Kosmos is a useful tool for Windows users. It allows you to render maps without extensive technical skills, and the rules are relatively easy to read on the wiki. You can use it to produce bitmap images of the size you want, in the style you want. However, it does have some bugs, only runs reliably on Windows, and isn't being developed any further.
Osmarender is the most powerful and flexible renderer we've looked at here, but also the most difficult to operate and customize. It uses open technologies and tools and can produce very finely...