I inow and have worked on yards where people put plants in and either did not know they would get bigger or just how much work it is to keep them trimmed and look decent.

Three hours sun is not very much and what ever you do go for plants that tolerate shade well.

What will you put on the ground for mulch?

The area appears to slope heavily in two directions.
After a heavy raing it looks as if you will get some washout.

I'd go for a mix of large hostas and some colorful blooming (shade loving) companion plants. Maybe see the list and pics on this Better Homes and Gardens online article (link below):

Here is a link that might be useful: Colorful perennials for shade

Hostas are a great suggestion. Large leafed and easy upkeep. The variegated species (more than one color in the leaf) would be ideal to pull the eye towards this feature.
Many hosta bloom in July, so look for other plants with different blooming seasons.

Other part-shade AND easy plants are
Astilbe (flowers mostly July; pest-free, low maintenance)
perennial geraniums (Lancaster, for example; sooo easy, also pest-free, fast growing mounds, flowers once mid-late June then when cut back one third will usually bloom again end of summer)
Hakonechloa (perennial Hakone grass, bright yellow trim on long leaves, spectacular punch to any shady garden; slow-growing clumps, airy allure, prefers rich moist soil)

So do your research and don't forget to mulch! :D

p.s. Just curious: ever thought of leveling off this bed with an added retaining wall of sorts? Just a thought...