Best plants for border between neighbors

Hostas might be good, and they do get flowers,

There are really pretty leafy bamboos you could use

You could use decorative grasses or shrubs that would grow together creating a hedge. Boxwoods are great for hedges.

you could also do a pallet fence, then put plants in between the pallet sections randomly

I live in the South and don't know your zone, BUT if I were you, I'd check with a local nursery and they could best advise you. Here, we use privit hedge and that might work for you as well.

We have burning bushes. There aren’t any flowers but the leaves are red in the summer. There are little red berries on them.

i personally love dwarf holly. Beautiful and spikey enough to discourage animals.

I just saw this on "Garden Smart" Sunday 2/24. They showed a shrub called Lespedeza, or Hardy Bush Clover. It grows 3 ft high and 3-5ft wide, hardy to zone 4. Has little purple flowers and get very dense. The gardener said If you can't grow Lespedeza you might as well put in a tennis court.

Spring is here. I’m sure the garden centers in your area will have something perfect.