Container shrubs

Dwarf Rhododendrons and Azaleas, Japanese Acers - though like the shrubs you already have they will eventually out grow the containers.

Almost anything will go in a pot but as MG says they'll all need repotting. I think I'd just bear in mind that it won't be permanent and pot what you fancy. Fruit like Blueberry currants or even roses will be ok. Watering could be a problem and wind too if the pot is small. If the pots are big you'll find it difficult to move them. sorry to be so negative. I'd be inclined to go for Fuchsias Pelargoniums maybe Formium. A small managable amount perhaps.

I'd recommend you buy the largest containers you can find - much more successful than little pots, easier to manage to, and better results from the plants. If the pots are round, and you think you want to move them about a bit sometimes ,you can get wheeled sort of trays for them to sit in so you can push them about.
Phormiums do well in pots, though you will need to turf them out every now and then and split them, then repot (probably every other year). Fuchsias can be dodgy as they're sensitive through the roots to frost, but okay if you protect the pots in the winter.
Otherwise, the world's your oyster, really - I'd choose mainly smaller shrubs, like Convulvulus cneorum, lavender, smaller Euonymus varieties, smaller hebes (like you've got, Acer palmatum (shadier spot though), Spiraea Goldmound or similar. Palms like Trachycarpus fortunei. Shrubs for shade, Skimmia, Pieris (good pot subject, use ericaceous compost) Camellia (ericaceous again), heucheras, Hostas. Fatshedera lizei is good in shade if grown against a support, like a fence. Fatsia japonica in shade too, though this will eventually get too large for even a large pot, but you'll get a good five years out of it.

A fantastic selection there Jonezze, just one thing, don't buy a pot that curves in at the top as you'll have a right job getting your plant out,

Good point Heron we've had to smash a pot before now!

bamboo either black or gold look very good in tubs, you need to have large pots-- so that they don't blow over! and use a plastic one inside so that you don't have to break them, watering is always a problem with pots and the bamboo especially benefits from a top dressing of white gravel
ours sound lovey in the breeze and make nice patterns in the sun