I would say sweet peas and/or sweet alyssum. I grew them last year and they smelled great!

Nicotiana, moonflowers, dianthus, some petunias, and violets come to mind. In your cool climate, you might be able to grow sweet peas all summer. (Lucky you.)

I'll try sweet peas. I've seen a burpee packet the other day. The description I remember is "very fragrant".

Thanks!

Do I still have time or am I late to sow sweet peas here in zone 5a?

Sorry, forgot to ask. Do they smell like the scent of Korean Lilac's flower? I can smell it from 15-20ft away. Is sweet pea the same?

HELIOTROPE!!!!! (they perform beautifully in partial shade, in my experience)

Do they smell like the scent of Korean Lilac's flower?

hmmm... I am not sure how to describe smell/fragrance, but yes, I would say sweet peas and sweet alyssum belong to the same category of fragrance as lilacs.