Black and white photography works very well with portraits. In part, this might be because many iconic portraits from the last hundred years are monochrome and we are familiar with the style. But it is also because when the colour is stripped away it leaves us with character and personality. Adding side lighting is particularly effective as it gives strong contrast between highlights and shadows.
Architectural photographs are often shot in monochrome to emphasise the shape of the buildings. The increased contrast possible with black and white over colour suits the subject well. These photographs are often taken in the early morning, partly to avoid the distractions of traffic and people, but also to take advantage of light from a sun low in the sky. This light throws long shadows and can produce attractive texture when it falls across rough stone or concrete. These images can also often benefit from the simplicity and stark nature of black and white.
Photography at night is worth trying in both black and white as well as colour. Often the yellow glow of street lights brings a scene alive. Alternatively, the texture and patterns in a scene are shown to better effect in monochrome.