Now what shall I plant in here??

Is it a sunny or shady site? From the pix. it would appear to be sunny. Are you wanting herbaceous planting or something different? Personally I'd be tempted to plant wee rhododendrons and other ericaceous plants plus spring and summer flowering bulbs.

Hi, Moongrow, yes it is sunny and very warm in the Summer.
I'd like a bit of medium height in there, but the soil isn't acidic. Also something that would take me through Winter without dying right back, other medium height shrubs in that border are Weigela, Spirea Anthony Waterer and a Buddleia.

If you are prepared to put in some ericaceous compost then Leucothoe curly red or leucothoe scarletta are very good for providing colour in winter. They are evergeen, and have some red foliage in summer, but much more so all through the winter. I have two and they seem to like the sun.

Cornus are good for winter interest with their brightly coloured stems and the red stemmed variety look good with the dwarf blue green conifers such as juniperus squamata blue star or the dwarf conifer picea pungens procumbens.

Thank you weedfingers, I like the sound of the Leucothoe and the Cornus...especially with the red tones in them. I'll get some ericaceous compost too as the soil in the summer is dry and dusty near the wall.