Not sure if you're after perennials or a shrub, but have a look at Nandina . . . lovely evergreen with leaves that change to bronze/red shades throughout the year (one type grows to 6ft, the other only 3ft). Perfectly happy in sun or shade!

How about Chaenomeles or Garrya elliptica.

Eupatorium/Ageratina chocolate grows quite tall, possibly more of a foliage plant but with small white flowers late summer. :)

Solidago, Golden Rod I always call it, late summer/autumn flowering, sometimes invasive but not in my garden ( as of yet) butterflies and bees love it...

Cynara cardunculus

Acers are lovely, but need an acid soil.

Should have made the question clearer [oh how often we comment on poorly asked questions and I am guilty as ever!]

Perennial /herbaceous for preference as there are already shrubs in the border.
I am pulling Solidago out by the bucket full. it has gone mad in the borders so you are lucky lincslass.

Chaenomeles is already in further down, in fact I have 2 in that area Volunteer.

Nandina looks lovely but the RHS book says it is frost tender and as this is the coldest windiest bit of the garden I 'm not sure it will be happy. Where are you located ? Sheliabub

Cynara always look stunning Botanic but I thought they needed full sun to be anything like decent.

The Eupatorium is a possibility, I have E cannabinum in another part of the garden. Another one would be nice.
Thanks for the suggestions.

I was trying to think of something to contrast with foxgloves and aconites - what about acanthus - big and spiky! I've seen it growing in some gloomy corners.
I agree with pulling out solidago - the smell makes me feel sick.

Oh dear, lol, mines been in approx 4/5 yrs and has hardly grown, I'm lucky if I get 3/4 blooms a year, I will leave it where it is then as I had considered moving it....

should alo have said I am on chalk so I don't want to have to go tending it too much. I 'm tempted to get a Rhodo for a pot as it do like them Diane.
Lincslass would you like some of mine? its an old variety and every section flowers without fail every year. If yes send me a pm.

Acanthus argh! I'm trying to get rid of it from another area of the garden. it is too thuggish sadly as I do like it. same with the older taller Jap anemones that's is creeping nicely/nastily [?] through a border too :o)

How about Thilactrum? And Verbascum?

I meant Thalictrum ...will take more water with it next time

How about Aruncus (goats beard) I split some last year and moved into the wood it's doing really well, or telekia it needs moisture or it whilts but mine grows under trees, I think I might have seed in my box ;-)

Oh I'd forgotten Thalictrums I have a double but there are some other nice ones.

Flavum Glaucum is a lovely one if you'd like seed pm me.

I'm located in North Herts Seaburn - and amazed to hear that Nandina is "frost tender". Never had any trouble with mine, but I can see you might want to be cautious.

I have 2 Nandina Richmond and they have survived in my west mids garden, they did look dodgy the year after I planted them ( the 2011/12 winter) and did have to trim a few dead branches/leaves off but they pulled through and have been fine, I have one south facing fairly sheltered by fence and one west facing which does get a bit more winds, but noticed you said its the coldest part of garden so yes might be risky :)