Herbs are really tough for slopes but tend to like sun- oregano, marjoram, thyme, and rosemary. They grow on our ramp with very little water, and even like poor soil.

Some really tough groundcovers- Symphytum grandiflorum- ground cover Comfrey; Geranium macrorrhizum and some of the other hardy geraniums; Heathers; Hypericum calycinum. I mixed some on a bank and let them fight it out.

On the slope in partial shade try creeping jenny, just buy enough to cover it, it will spread slowly in poor soil, but it is really nice. It will turn red in the winter for you.
In the sun, buy some sedum and ice plant, both. They will both spread good for you and you won't have to worry about constantly watering them all summer long.
You can buy both of these in the spring at any home center, they have nice varieties to choose from.