Not ever green but I like a Green Beech, Fagus sylvatica, hedge is considered one of the best garden hedges and when clipped Green Beech hedging holds its leaves - which turn a beautiful russet colour in the autumn right through the winter. We have a lot of them around here- lovely.

I agree with Beech too, it does make a an excellent hedge. Hornbeam (Carpinus betulus) does a similar thing too and is slightly quicker growing though the retained leaves in winter are less warm/russet in colour than the Beech.

You don't say how high you would like your hedge. Some types of hedging plant suit certain trimmed heights better than others. Lonicera nitida 'Baggescens Gold' makes a dense evergreen hedge of small yellow/lime green elliptical leaves and can be trimmed to topiary quality if wanted. It's great for hedges no more than 5ft 6ins or less and surprising fast growing.

An unusual evergreen that might be worth looking at is a New Zealand plant called Griselinia littoralis. It makes an excellent hedge though best if not in too cold an area.

As you are wanting an evergreen hedge, I'm with Fractal on the Lonicera nitida ' Baggesen's Gold'. Another one to consider is Yew (Taxus baccata) but parts of the plant (esp. the berrries) are poisonous so not recommended if children are around. Alternatively conifers such as Thuja occidentalis 'Rheingold' can be kept quite neat and trimmed to whatever height you want - it also an interesting colour mix of yellow / lime green with a red tinge to the leaf margins.

And I'd add Photinia fraseri 'Red Robin' to the list, very attractive evergreen with bright red new growth.

Thanks for your replys eveyone - very much appreciated.