Euphorbia - or Wood Spurge
I love euphorbias, so much that I'd love to have a whole garden of them, well perhaps even a large area.  Why?  Well, they're easy, there are one for every area of the garden, they don't require much looking after.  Also, once established they provide good ground cover and spread over the years - and there are such wonderful colours.  

E.Griffithii - one of my favourites

Here's some information about them which was taken from The Guardian newspaper recently:
"Euphorbia suit every situation from desert to bog, formal courtyard to wild woodland. With one or two exceptions (see below), euphorbia are dead easy. They are also terrific value in the garden, the colourful bracts lasting many weeks.

E.Fireglow

In fact, this family has only one bad point – an irritant sap that bleeds from the plant when it is snapped. Wear gloves when handling euphorbia, and be careful not to touch your face or get it in your eyes.

For the Mediterranean patio

The acid lime E. characias and blueish subspecies 'wulfenii' are upright evergreens from the Mediterranean. Both look marvellous with paving – perhaps because so many seem to grow out of solid rock – and equally good in borders. The stems produce foliage the first year, then chunky, yellow-green flowers the following spring. New shoots spring up from the base, so there is fresh growth every year. The species grow up to 5ft tall and wide, and have given rise to many excellent cultivars, includingE. characias 'Lambrook Gold' – hefty, with whopping golden heads (1.2m); E. characias 'Black Pearl' – elegant clumper, with sultry, dark brown eyes (90cm); E. characias 'Portuguese Velvet' – really good form with blue-grey felty leaves (50cm x 75cm); E. characias 'Humpty Dumpty'– dwarf form, 30cm high. Sadly, some of the most handsome forms are short-lived – I have wept to see 'Black Pearl' keel over after five splendid years for no apparent reason – but they seed about when happy, so you'll have another.

For patio pots
Seek out E. 'Diamond Frost' (above), with clouds of airy white flowers and frondy foliage. Usually sold as a bedding annual, it is, in fact, a tender evergreen perennial and can be overwintered in a greenhouse or on a windowsill.

For the rock/dry garden

All the above thrive in hot, dry sites, but primeval-looking E. myrsinites (below) is a show-stopper, with trailing stems of blue-grey fleshy leaves and lime flowers in spring that turn delicate pink as they fade (10cm, up to 1m spread).

For woodland or dry shade
All forms of E. amygdaloides enjoy shade and humus-rich soil, butE. amygdaloides var. robbiae (30cm), with shiny rosettes of dark green, leathery leaves, romps away in the darkest, driest shade, lighting dark corners with bright lime bracts in spring. For lighter shade, chooseE. 'Whistleberry Garnet', with rounded clumps of red-edged leaves.

For the bog garden
Though not evergreen, E. griffithii 'Dixter' and 'Fireglow' deserve a place in every garden with damp soil. Dark green leaves are flushed red in spring, then turn red and yellow in autumn, following the brick-red summer flowers. 'Dixter' is smaller and neater (70cm); Fireglow is brighter, especially in full sun.

Big and bold
With gleaming, white-ribbed leaves and huge, fragrant, amber bracts,E. mellifera can reach 2m round, but may be hacked back in spring to new growth produced from the centre. Described as half-hardy, it has survived lows of -12C in my garden. A warm, sheltered corner is ideal.

If you want a purple one...
E. amygdaloides purpurea (below) looks so tempting in the garden centre in spring, with apple-green bracts on plum foliage. Spurn it – it is a martyr to mildew. Likewise, mahogany-coloured E. dulcis 'Chameleon', which is prey to rust. Go for sturdy 'Blackbird' (50cm) with red-black leaves on red stems and orangey bracts from April to June, or 'Redwing' (70cm), which flowers earlier and longer, over purple-flushed leaves that darken in winter.

Aftercare

Euphorbia look best if allowed to sprawl at will, but if space is limited, you may need to support the floppier ones. The evergreens require no routine pruning – simply tidy them up when they start to look tatty. Deciduous ones should be cut down to ground level in autumn. New shoots will emerge from the crown in spring. The biennial forms such asE. characias produce new shoots from the base each year. Cut out dead stems in winter. They are not fussy as to soil, but most prefer good drainage.

They grow well with...
The bigger, more sculptural forms look good with architecture – against steps or walls, or in corners of courtyards. E. mellifera is a superb statement plant. I grow E. myrsinites in a river bed garden with E.'Redwing', golden Libertia peregrinans and blue and gold grasses. E. griffithii 'Fireglow' looks marvellous beside water, with bronzy rodgerias and red-flushed astilbes, but will serve in any hot border, while E. 'Whistleberry Garnet' associates well with ferns, hostas and the dark-patterned leaves of Geranium phaeum."

http://gardenerstips.co.uk/blog/gardening/euphorbia-euphoria/
http://www.bbc.co.uk/gardening/plants/plant_finder/plant_pages/305.shtml