I love the effect topiary adds to the garden. It brings depth and structure, breaks up monotony and creates a mood. It seems to fit any scheme, formal or informal.
I've invested in a number of clipped spheres in recent years which are dotted around the courtyard and down by the river. I like the way they add dimension and scale and continue looking good in Winter.
There are many plants other than Box (Buxus) which lend themselves to be shaped or trained.
The 'standard' in the middle of this photo is a Privet (Ligustrum). I clip it every 6 weeks or so in Summer so it's a little faster growing than Box, but that's no hardship.
The spheres on either side of the pic are Golden Leylandii (Cupressocyparis Castlewellan Gold). They have both a beautiful colour and a superb texture.
Here you can see two shaped Thuya Aurea Nana, a golden conifer which I planted down by the river. Its' foliage changes from bright green to golden through Summer taking on a more burnished hue in Winter.