A few tough rhododendrons might be nice. There are some strains like PJM that don't require acidic soil.

I love the walkway with the pink flower border.

Rhododendrons look sparse and informal IMO. If you want to consider an evergreen groundcover, Pachysandra does well in both sun and shade and never disappoints, AND it is one of the few plants successful under pines. Vinca would do well too. You could always try another variety of boxwood, like the upright (I forget the cultivar name, perhaps the Green Velvet?). The left side looks somewhat formal (and that border is beautiful BTW), so I'd keep it formal on the right side too.

ack, just realized this is an old post HA

Still current enough to make valid comments :-)

And unless grafted onto Inkarho rootstock (which, to my knowledge, is not yet widely available here in the US), ALL rhododendrons require acidic soils.