Hydrangea annabelle goes beautifully with li
limelight.
A good lavender would smell gorgeous as you walk past. Or a curry plant as also smells amazing (needs pruning to keep it in check though).
You could also go for something evergreen and more structural, yew is brilliant and you don't need to keep on caterpillar watch as you do for box.
Ornamental grasses look beautiful, give lots of soft movement and sound lovely in the breeze.
I'm a big fan of ferns, too. They're easy to control and look great - add lots of interest and really low maintence.
Flaming dogwood - great for winter colour.
Or you could look at a dwarf tree or rose. Sticking it in a pot could add extra interest, especially if you stick a few bulbs or some creeping ground cover around it (thyme, chamomile etc) as well as limiting its size.
Have a look at other herbs too, like rosemary or oregano, it doesn't need to be shrub to work in the space.