I do not such plants. But what you can do is to plant some in intervals.
(1) very early; and plant one that fruits a bit faster
(2) plant some when the first one has fruits alreay;
(3) plant some down the road. you might look into variety that likes cooler late sumer/early fall weather.

About peppers - although my zone 10 is near San Diego. However, these peppers may be perennial for you as well. It was a bit frustrating because I planted quite a few this past year (around April 2009) - all were healthy - no problem growing them. The only thing is that they were sooooo slow to turn red. On the bright side, they finally did, and I am still harvesting peppers - would you believe! Although even tho slow growing, they kept a steady yield coming in. In a warmer climate, they probably would have "reddened" all at once.

I grew - mainly the Anaheim - ancho type, which taste a lot like the green bells, without all of the problems growing them. I was mainly interested in making stir fries, dehydrating, powders, and Mexican dishes - not stuffing them anyway - so opted for them instead of the bells.

Also grew Thai hots - (whew), which to me are even hotter than habaneros - (drying these for stir fries, powders, etc.).

A few jalapenos - which I froze - after blackening skins, peeling and putting in citric acid and salt (for Mex-type dishes - taco fillings, etc.)

Poblanos - used same as anchos.

A paprika type - that I forgot name of - (for dehydrating and drying).

Also some multi-colored hots that look like X-mas lights - forgot name. Still bearing strong, inspite of cold temps now.

All of these plants were planted last year - around April - and I just cut them back - as they have new growth coming on now.

I have never bothered to try to keep them perennial - (planting new plants when I set out tomatoes), but as you can see in our zone, you may not have to re-plant new ones -although I've personally not left mine in for a 2nd year's growth. They do, however, grow over a long period of time and are very hardy.

My main reason for pulling them - is to make room for other things that I want the space for - as I grow year-round in small 4 x 6 ft. boxes - intensively.

Probably more than you wanted to know but our warmer climates gives plants a longer lease on life - sorry to be so long-winded.

Bejay

CB

Unless you planted three of the same variety of DETERMINATE tomatoes, you should have been able to harvest tomatoes the entire growing season -- that's if you planted the same INDETERMINATE variety.

So, I'd think you're looking for vegetables that are early, midseason, and late, as cyrus_gardener mentions. That's easy if you are willing to start your own seeds, OR if a local store has enough varieties that you can pick and choose among them.

Bell peppers, once they begin production, will give you fruit until they die from disease or the weather. You might be able to find an early one to produce all season for you, thus giving you an early harvest that continues. If you want variety, you can always look in seed catalogs for the days to maturity (DTM) for vegetables and choose a couple of short- and longer-season vegetables for each plant you'd want to grow. Start or buy those.

You can explore the characteristics of tomatoes and bell peppers here.

Summer squash are usually very quick-growing, around 50 days, and they, too, will continue to produce if the insects and weather don't do them in. Johnny's features the squashes on this page that you can check out. Many other seed companies also sell squash seeds.

You are lucky if you can buy the plants you want to grow locally. But seed starting is fun, too!