When frosts hit will have a huge effect. Sweet alyssum is still doing great for me, BUT we haven't had any frosts yet. Most annuals don't deal well with frost. Zinnias are starting to look a bit ratty -- though still blooming. Can't complain there, though ... they bloom great all summer long.

Marigolds hold up very well to heavy frosts.

Now that I think of it, my neighbor’s Nasturtiums are still looking really good, too.

Geraniums (annual ones) do quite well when the cooler weather sets in -- they don't usually start looking bad until after a light frost; even then they don't look too bad, although of course a heavy frost will do them in. I sometimes just buy potted mums and slip them in pots for the porch/patio, the other annuals poop out come September or so, and some just don't tolerate cooler weather (we've had a couple nights in the low 40s already).

I’ve had good late season color with geraniums before, but mine didn’t do well at all this year, even after I got the budworms under control. One or two were decent, the others never really took off. I only have one blooming now.

The mum season is so short, i can’t justify the expense. i tried perennials in containers this year, and am happy with the result so far, will consider keeping and tweaking them for next year for my planter inserts. Expensive way to go if planting every year.

My petunias are still gorgeous, but I fought the budworms on those all summer as well, and had to spray weekly.

Lobelia and calibrachoa are my two all season favorites. They're actually perennials, so they handle the cool weather in October and November quite well for me (zone 6/7).

At least with in the ground plantings, I've had mums return for years up at my folks' place (zone 5/6). Interestingly, some colors seem to be hardier than others. The purple flowered ones have proven the strongest/hardiest. Those at my folks' place are well over 10-15 yrs old.

Dahlias start blooming in summer and are at their peak in the fall. I love mine this year.

I still have blooming (no frost yet, but temps close to it):

Zinnia angustifolia (religously deadheaded for continual bloom)

Calendula

Salvia of all sorts of red

Lemon gem marigolds

Browallia

Lantana

Fountain lobelia

Feather celosia

California poppies

For me my Petunias and Sweet alyssum always seem to thrive in this cooler weather, even with light frost as long as they receive a good amount of direct sun.

Angelonia is another one that works non-stop for me until the first heavy frost of the season.