Aster laevis blooms around the end of August.
Aster alpinus Alpine Aster blooms early around the end of June, early July.

Aster sedifolius nanus, blooms around August.

Around September...
Aster novae-angliae
Aster dumosus 'Anneke'
Aster novi-belgii 'Professor Anton Kippenberg'

This dendranthemum can be spectacular in the fall - Dendranthemum rubrum 'Dutchess of Edinburgh':
{{gwi:542778}}

My Michaelmas Daisies (Aster novi-belgii?) are great in the fall, but often don't bloom until September. I think this picture was taken in October.

Connie