There's plenty of time before the average first frost hits. And several plants do well even after that date. Here in Chicago it's October 14th, (or is it the 22nd?). I'll split the difference and say the 18th. Keep in mind it's weather, and these are averages.
Here's a chart that shows the last starting dates for different plant varieties, given a specific first frost date. If you start today, you have enough time to grow the following:
Bush beans, beets, broccoli, brussels sprouts, cabbage, carrots, cauliflower, chard, collards, cucumber, kale, lettuce, okra, peas, radishes, spinach, turnips.....
I'm sure there's more I've missed.
Google to the rescue:
WHAT TO PLANT
In general, vegetables that grow best in cool weather are leafy greens, root crops and various members of the cabbage family. Beets, carrots, peas, chard, endive, kale, kohlrabi, lettuce, turnips, radishes, spinach, oriental vegetables like Chinese cabbage and bok choy and transplants of late cabbage, broccoli, cauliflower and Brussels sprouts may be planted in early August for fall harvesting.
My fall plantings of lettuce are healthier and better tasting than the ones I harvest in early spring. When I plant cauliflower in early spring, I get small, ricey discolored heads; when I plant for the fall, I cut snowy white heads with excellent flavor. I have similar good results with fall plantings of Brussels sprouts. When choosing cultivars for harvesting in the cooler temperatures and shorter days of fall, look for characteristics such as cold hardiness and quick maturity. Some cold hardy cultivars for broccoli are 'Waltham' and 'Green Valiant'; for Brussels sprouts there is 'Jade Cross'; for cabbage, 'Danish Ballhead' and 'Savoy Ace'; for cauliflower, 'Violet Queen' and 'Snow Crown'; for lettuce there are many choices: 'Black-Seeded Simpson,' 'Four Seasons,' 'Oak Leaf,' 'Salad Bowl'; for peas, there is 'Wando' and for carrots, 'Napoli.' Check seed catalogs for other recommended cold tolerant varieties.
Adams County Master Gardener
We've had success with seeds from Victory Seed Company and Seed Savers. It's not rocket science. In fact you probably did it when you were a 2nd grader, which means you'll have no problem doing it now.
Here are two good links for more information on seed starting.
And if they don't have what you're looking for, this 300 page pdf The New Seed Starters Handbook should.