One of my favorites is Torenia which is at home in a part sun environment.

Yes !! Torenia.
If planted in loomy soil will spread and fill a large area.
Also mine have reseeded and 1/4 returned the following year.
They were located in a area that gets 4 hours morning sun.

For return flowers try Forget-me-nots.
They fower now and small amounts through the summer plus spread by reseeding and come back every year.
Here's mine yesterday where I transplanted only one of them last September..
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Polemonium/Jacob's Ladder does well; I have a few in a shaded bed. In the same bed, I grow an unknown clematis and Tricyrtis/Toad Lilies, as well as a fern and some daylilies. From what I can remember, there's very little, if any, direct sun.

Before you completely "pass" on impatiens, see if you can
find the sometimes hard-to-locate darker purple variety...
it's my favorite for cool shade...other annuals for partial
shade include browallia (true blue), Salvia farinacea
(mealycup sage) and lobelia.

The list of blue or purple perennials for partial shade is
pretty extensive - some of my favorites: Mertensia Virginia blue bells); Aconitum (monkshood); any number of
Hydrangea (but particularly H. serrata 'Blue Billow');
Lobelia siphlitica; dozens of Hosta have pale lavender flowers; there are several blue Aquilegia; the geraniums 'Johnson's Blue','Rozanne', Samobor' and 'New Hampshire Purple'; Lamium 'Purple Dragon'.

I 2nd the geranium 'Rozanne' recommendation because its so easy to grow, a pleasing blue-lavendar flower color and flowers non-stop all summer. Also I've never seen deer or rabbits touch it. Its leaves are finly lobed and its elegantly sprawling in its growth habit, so you may want to pair it with small-to-medium sized hostas to provide some contrasting substance & structure. Although not known for their flowers, depending on the variety, hostas bloom in shades of white to lavendar, working well with 'Rozanne'.
Lisa