Sounds like a good place to throw a couple of packages of pernnial seed mixes from the nursery & water in & fertilize with some liquid plant food once a week or so. I'm going to do that in bed where i usually grow tomatoes, time to give it a rest & will be fun to see what comes up. Don't want plants higher than below the vehicle side windows 3-4 ft. so take that into consideration.

The possibilities are almost endless, but here are some that have done well for me in a bed that gets sun most of the day, and all afternoon.

Daylilies love sun. Most are between 18" and 36". Choose a rebloomer (most would bloom twice in your zone, particularly the early and mid-season bloomers) or "extended bloom" varieties like Stella De Oro, Happy Returns, Rosy Returns, etc. (which bloom almost all summer). Flower size, shape, color, and pattern are remarkably varied (don't expect a real blue, though -- or a pure white). For a really good selection, visit a local grower or mail order from vendors who specialize in daylilies. [The general seed-and-plant mail-order companies that sell a few daylilies are usually priced way too high. Specialty daylily vendors will usually give you much more plant for your money. Don't be shocked, though, at the prices for some of the latest and most expensive varieties: you don't have to buy those!]

I like gauras. 2-3' tall, very enthusiastic. Odd 4-petalled flowers which dance in the breeze; often compared to butterflies. The petals wilt in late afternoon, but still look interesting from a distance. Most are white or blush pink, but I've also seen some in the red shades.

Shasta daisies (various heights up to about 3'). Mostly white, but a few yellow cultivars.

Coreopsis. I have some 12" babies, but most are much taller. Generally yellow; sometimes solid red, yellow with red, or white.

Most foxgloves are biennial rather than perennial, but if you let them go to seed, they'll keep themselves going from year to year. Low foliage and tall, impressive flower spikes, in a wide variety of colors (heavy on the lavender and rose) and generally 3-5' tall.

Herbs like thyme, rosemary, and lavender will provide some winter interest. Thyme is generally 1' or less; most have lavender flowers, but the creeping cultivars have other colors (red, white,pink, and I think yellow?). Rosemaries and lavenders are various heights. I think rosemary flowers are only blue-lavender, while lavender flowers are in the blue-to-purple range except for a couple of white-flowered varieties (I have one with white foliage as well). Some of these may not be perennial in zone 6 (the prostrate and cascading rosemaries won't live through the winter, though the upright cultivars probably will.

How much clearance do you have for opening car doors or walking around the vehicles? If taller growing plants will interfere with car doors and access or are likely to get whacked if car doors open onto them (not to mention kids jumping out, etc.), then I'd probably focus on groundcovers or other very low, spreading plants. Often, these can take a good deal of foot traffic and abuse yet still offer color and flowers. And remember that bees are attracted to flowering plants so they can pose issues also.