Jojoe I like golden creeping jenny its easy and will do fine in sun or shade. This is the type of plant that if a stem breaks off, you put it in moist soil and it'll be rooted in no time! So, you can spread these around from a small amount of plants.
Creeping thyme is nice for its fuzzy leaves.
Another easy one to grow is Lithodora (there are several colors of flowers and they tend to have a long bloom time)
All of these are very easy to grow in Seattle, so I'm guessing they'll do well there too!
I can't remember if your bed is in full sun or part shade?
I'm thinking with your summer heat, these may get burnt if in full sun...so planting them on the shady side of rocks, or under taller plants may be good to provide some shade. As usual please take photos when you have some plants planted!!
