Hi pck081478, you can start all perenial flower seeds off in the fall, this is the best time to do it as there is still enough heat around for germination to take place, but at the same time, the really hot weather wont dry out and burn the new emerging plants, also you can start Biannial seeds as they need one season to germinate/grow and the next year to flower out in the garden, things like wallflower for instance. you dont say if you have somewhere to keep the seeds indoors over the winter, this is a must for your temps as the seeds will be too soft and tender to withstand the cold winter and all your effort will be waisted, if you pop into your librery or book store, then there are books to help you understand what you will need to do as for germination, pricking out, and potting on till they are large enough to plant out in the garden the next spring. It is one of the most satisfying part of gardening when you plant out flowers or food you have grown yourself, so read up and dont be too worried if things dont look like the ones you buy from the store, we are all just amatures so good luck, lots of happy gardening. Weenel.
You can plant Erysimum cheiri aka English Wallflower, Common Wallflower right now, if you can find the seeds. They are usually available by mail order. http://davesgarden.com/pf/go/1562/ It is widely used in Europe as a companion to spring bulbs.
I had great success sowing seeds in winter in plastic jugs. Lots of plants' seeds need the cold temperatures to break dormancy. It was inexpensive ( just bought soil-less seed starting mix) and I grew enough plnts to fill a 40' x 5' bed, and then some!
This site tells you everything you need to know about winter sowing:
Sorry if I got carried away with the pictures, I'm very enthusiastic about winter sowing!
And I know you asked about fall sowing - but if you sow seeds in winter, they won't sprout until they're ready, and the plants are very hardy that way. Frosts can come and go but the plants live right through it, no problem. That's snow on top of the jugs in the first picture, and there were hardy geranium seedlings growing at the time. I've already collected seeds from those plants for next year.
If you sow in fall, the seedlings have to face a long winter, instead of gradually warming temperatures and more hours of daylight. The only drawback to winter sowing is some people don't like transplanting all the little seedlings, but you can plant them in little clumps.