Low clipped hedges of Box, Rosemary, or Lavender are used to edge flowerbeds in the most formal of gardens in the European and English styles. Tall hedges, clipped or not, are primarily used for privacy or to divide the garden into 'rooms'.
There is certainly no need to limit your choice to the commonest form of hedge, Privet - let your imagination flow. Any bushy shrub that can withstand regular pruning can be used. If you plan to clip regularly, those with smaller leaves will inevitably look less mutilated.
Even tall trees can be used as garden hedges as long as they can tolerate the constant clipping - Yew and Cypress are commonly used. Hawthorn hedges work well with their branches interwoven 'basket style' to make them impenetrable. This was a common feature of the English countryside prior to modern agriculture that has led largely to their demise. In the average garden however, small and medium shrubs are safer and less work.
A clipped 'tapestry hedge' with the foliage display of two or more different plants woven together can provide a pleasing effect. You might try combining Viburnum TInus with the red young leaves of Photinia for a rich effect.
To create a clipped garden hedge, you must prepare your soil well first. Then plant your plants at a spacing of around one third of what would be considered normal. For a standard Box edging, plant about 30cm apart. For a head high hedge of plants such as Camellia sasanqua, plant your shrubs around 1 metre apart. Stake the plants if needed to maintain form and water and fertilise as usual.
It's tempting to encourage the plants to grow up to their desired height as quickly as possible, but you must be patient and keep the plants bushy by pruning their flanks. If you let the shrubs get leggy, and bare at the base in the early stages it will be difficult to encourage them to fill in later.
Once the final height is reached it is a simple matter of clipping. Slow growing shrubs often provide the best end result so exercise patience. Rapid growing plants such as Privet require far more maintenance and constant discipline to achieve the desired results.
To rejuvenate an old, tired, overgrown garden hedge, cut it back ruthlessly to its proper shape and give it some fertiliser and water. New growth will soon come through and cover the butchered appearance. Be very careful though as some conifers for example will not grow back if you cut into the old wood. If your old hedge is a Cypress variety you may be better off starting from scratch.
A well maintained hedge can last for centuries. Indeed old boundary hedges in Britain may be over a thousand years old. But modern garden hedges are often created from a range of exotic plants and may not look good when they get old. They become too thick, gappy, full of weeds or diseased and you may be faced with the options of removing them or trying to restore them to a more useful and attractive state. So just what kind of restoration is possible.
For most conifers the possibilities are limited. When old they are usually green on the outside but the inside of them is brown, old wood. With the exception of Yew these old conifers will not re-grow if you cut back into the brown branches. They will remain brown and an eyesore. Yew however is capable of growing from brown, unpromising wood although decent regrowth may take a year or two. To restore such a Yew Hedge it is recommended to undertake the job over a couple of years cutting back one side at a time. The best time to undertake this is in spring when evergreens tend to be less active.