hmm...

if you feel like putting up a trellis there (or a post at either end with wires strung between them) it's an ideal place for one of the hardy kiwi vines- I know one likes half sun, and one needs true shade.

smaller hostas, especially the striped kind, would look nice, and tend to stay neat and orderly looking for years.

Lamium (dead nettle) is a great silver-and-green groundcover that spreads readily, and has varieties that flower in pink, white, and lavander.

woodland phlox make amazing, fragrant 'fairy wands' of lavander blossoms in the spring, and the rest of the year is a compact groundcover.

a nice moss bed studded with interesting standing stones would also be pretty, and if it's not weedy to start with, would be a low-maintenance idea.

ferns are a great option- ostrich ferns have a nice upright habit that would fit in there great- and if it gets ANY sun, they can grow 4 feet tall (otherwise, 2.5-3')japanese painted ferns are my favorite, though- they can really light up a dark corner.

you can also look into the coral bells family- the foliage is the big thing, ranging from gold through bronze to burgundy and silver (the golds are new, and running $15 a gallon up here. the burgundies are garden staples, and can often be gotten from other gardeners)

I have a very small shady area that I put some lungwort in and it has done very well. Nice lance shaped green foliage with silver spots and pink flowers in the spring. Thye have also been able to take several weeks of 90+ heat since they were established in the spring. Individual plants only get to be about 1'x1'.