Paniculatas would be fine in full sun, and there are a number of lovely cultivars to choose from. Also stunning would be some viburnums--you'd have berries in late summer. My favorites are the tea viburnums--V. setigerum. No named cultivars, but you still need more than one for proper pollination. V. setigerum gets about 10-12 feet tall, is narrow, but tends to get naked about the knees as it ages, so something lower (4-5 feet)in front works well. Also nice are V. dilataum 'Cardinal Candy'; they'll need a pollinator too, and V. dilataum 'Asian Beauty' makes a good one.

Another stunner for late summer is Seven son flower--Heptacodium miconioides--a small tree. Look for older posts discussing this plant.

Weeds are going to be an issue pretty much whatever you plant. The worst weeds in a shrub border are woody ones that can't begin to survive in a mown lawn, so they kind of sneak up on people.

What you need is a weed strategy, not a shrub strategy. Heavy layers of newspaper or cardsboard covered with mulch work well. However, they break down and need to be replace periodically. Also, the squirrels will dig holes in the mulch and plant things.

I have a mess of shrubs, mixed with the perennials. Included are Callicarpa(beautyberry) and dwarf Ilex verticillata(Winterberry)and Viburnum nudum 'Winterthur". For differing reasons, the Viburnum and Ilex must be near to closely related types, to allow for the decorative berry production. Berry bearing Ilex are females that need a male, nearby, that blooms during the same weeks. Viburnum bear better if they have a different sort, of the same species, nearby.

If you want late season bloom, how about Rose of Sharon? It is a type of hubiscus. Sorry, I don't know the Latin name.

Teresa

It's Hibiscus syriacus and I was going to suggest that too but I don't know if it is hardy in Zone 6. Ceratostigma willmotianum and Perovskia are both late summer bloomers but again might not survive a NY winter. The same may apply to the hardy fuchsias which flower their head of until frost in my garden. Another candidate is Clerodendrum trochotomum. And don't forget berry bearing shrubs for colour and wildlife interest. Some of the Eunymous would give you berries and leaf colour.

The Bush Clover is stunning in late August and throughout September. Although it dies back to the ground like a butterfly bush I've been told. This is my first year planting one, so I'm learning.

I noted what shrubs I saw flowering on my walk home this evening: Hypericum patula (possibly Hidcote), lavender, quite a few different roses, hydrangeas, Magnolia grandiflora, Abelia, Viburnum tinus just starting to open and Skimmia japonica in bud. There are also a lot of berries about including Pyracantha. Also have you thought about using late flowering climbers? Solanum jasminoides is still going full throttle here and a few clematis are having a second flush. Some of the rugosa roses are still flowering at the same time as producing large colourful hips.

If you are looking for hydrangeas (paniculatas), may I suggest Limelight or Quick Fire? They are both fast growing, and tolerate full sun very well in my climate (zone 5b). They also have stunning and long last flowers too. My Quick Fire bloomed in June with pure white flowers whose white color lasted for months, and now, they still have these lovely mauve color flowers on display! My Limelight is also very showy, with these lovely lime/creamy white flowers that last a long time too. In fact, they are still coming out with new flowers! Great shrubs indeed.

Rose of Sharon, or Hibiscus syriacus, is hardy in zone 6. I think clerodendrum trochotomum is only hardy to zone 7. Another possible choice is Itea (Sweetspire). I picked up two today at Loew's for $5.25 and they get about 4 ft x 4 ft. My cultivar is Merlot and the color looks like it will be gorgeous. It is is supposed to have sweet smelling flowers in mid-Summer.

Teresa