If the garden is not too sunny, I'd go for heucheras too. You can get so many lovely variations of leaf colour and some have very pretty flowers - not huge but delicate in shades of white, coral and red.
If it is very sunny, how about lavenders? There are compact varieties that won't grow too leggy as long as you look after them.
Both heucheras and lavender are easy to take cuttings from, so even if you started with a few you would soon fill the space.