I particularly like the Amelanchier x grandiflora 'Autumn Brilliance'. AKA the Autumn Brilliance Serviceberry. It's got brilliant white flowers in the spring, edible red berries in summer and orange to red foliage in the fall. It also is a slow grower and stays relatively small.

Good luck to you.

Thanks for the response ... apple Serviceberry looks like a possibility. I have two concerns: 1) that it may not be substantial enough for the one and only place I have to showcase a tree and 2) though I love birds, that it will attract them and that they will deposit them in undesired places after ingesting. Your thoughts?

Many of the magnolias would work for you. A "saucer" magnolia is an incredible sight in the spring and they have large, pea green leaves the rest of the growing season. Some of the yellow magnolias would work for you as well like "Elizabeth", "Yellowbird" or "Butterflies". The little girl series of magnolia are outstnding trees as well. "Ann", "Jane", "Susan" and others have purple to pink flowers that are 6 inches across with a medim sized magnolia leaf. You could consider a Stewartia as they have a wonderful white flower that will cover the entire tree. They also tend to form a round tree and are excellent as a specimen.
You could consider a Paperbark Maple. They are an excellent smaller tree with cinnimon colored peeling bark that draws attention. The Tri-florum Maple is a relative of the Paperbark and is a fine tree with very deeply groved bark. They both have a trident leave and show well.
There are many crab apples that would work for you in this spot. Consider "Candymint", "Coralburst", or the weeping crab "Louisia".
The best of luck.

Acer triflorum though those are not common (had to bring in ours from outside), Acer griseum (both as suggested above) Venus dogwood, Milky Way kousa dogwood, Hear Throb kousa dogwood, Maressii Vibrunium, Nachez Crypte Myrtle, among others. Personally the dogwoods would give you multi-seasonal results. Flowers in spring, red berries late summer, long lasting fall color, and in the case of kousa dogwood, exfoliating bark for winter interest. Our Heart Throb kousa, the leaves have red edges and highlights at the current time. VERY attractive IMHO.

Arktrees

Kousa Dogwood or a Japanese Maple always make good center pieces. But if you want cars to crash in front of your house looking at your tree, plant a Golden Chain Tree! Only gets about 15' tall and 10' wide. The bark is green and the leaves are very unique. But the golden chains when they bloom are a show stopper in my opinion!

Got a couple more thoughts for you.

Acer leucoderme - Chalk Maple
Stays pretty small, has nice bark, tough, and great fall color.

IF you site is DRY,
Cotinus obovatus - American smoke tree. Great small tree/large shrub, unusual leaf color, some "smoke" when mature, and great fall color. Also native to our area. CATION:SITE NEEDS GOOD DRAINAGE, AND FAIRLY DRY. There is a small one located at Botanical Garden of the Ozarks in Fayetteville, also a larger one in front of the Washington Count Cooperative Extension office in Fayetteville.

Arktrees

Just a caution....zone 6a is a tad warm for Laburnum...mine gets scorched and leaves brown and curl by August, every year. Then it looks like it's dying. As a result, they don't root in well and require permanent staking. The older ones at Longwood Gardens, 15 min. from me, are beautiful when they bloom, but the stakes and webbing apparatus detract.

Well, after researching all of your suggestions, and even though it doesn't give me the evergreen screening I was hoping for, I'm pretty locked into the Venus Dogwood right now for the one and only special spot I have in my small front yard ... it appears to have multi-season interest and an incredible flower show in the spring and will end up being the perfect size. Am I crazy?

" Evergreen is OK but not preferable (though a Magnolia might work)"

Sorry, but you had said that you did not prefer evergreen????

Just the same, the Venus is truely a site to see in full flower. The only small negative is that the flower show is somewhat short and limited number of fruit set if you want the red fruit in August-September. It is also very disease resistant, and should do very well as long as you have reasonable soil (no standing water, does not stay wet for days after a rain, not hard packed). In addition, it should be very happy with our climate. So, not crazy at all.

Arktrees

Sorry for the confusion, but evergreen was my preference because I was hoping to also use this tree as a screen to block out my across the street neighbor. However, none of the evergreens (except maybe the Colorado Blue Spruce) hold a candle to some of the deciduous choices for 4-season interest, IMHO. The Venus meets all of the requirements to be happy in my yard. Sure, a longer bloom season would be great, but there just doesn't seem to be that absolutely perfect tree and at least the Venus is spectacular. As for the berries, that's plenty OK ... as much as I love birds, I try to avoid berries and fruit as much as possible because of the mess the birds leave behind on our cars and our rear deck. Thanks Arktrees for the continued replies ... nice to hear from someone in my grow zone.

Bill,
I'm happy to help. My previous response was just to make sure you understood those aspects. I thought you probable knew, but wanted to make sure of it, and for anyone else that might read this. FYI, I don't know where you are located, but there are Venus dogwoods available at the local nursery's (the one with multiple locations in NW Arkansas) in Fayetteville, but they are larger and rather expensive, but for a showpiece tree, it might be worth it to you. BONUS: They should be hitting peak bloom soon as well, so you can see them for yourself. Hopefully it will be a good year for them, though most dogwoods I have seen this year at nurseries have been short on flowers for whatever reason. If you don't mind starting from smaller, then they can be found online for less.

Lastly, I'm sure you understand this, but JIC. It likely will not flower normally for a couple years after you plant. Takes some time to recover from transplanting. Anyway, send a message if like.
Arktree

Have you considered a Magnolia grandiflora? Your posting says zone 6a (I didn't know Arkansas even had 6a zones). Some cultivars are more compact and hardier than others and nearly all only grow moderately fast at best. Then again these mostly tend to be broad trees. What about a holly? They offer evergreen screening and red berries in the winter.--One of my favorites is Nellie Stevens (very robust grower)--but again may go beyond your single floor requirement.--Though there are dozens and dozens of holly varieties.