How do you define "interesting winter silhouette"? Are you looking for a tree that will get large? How fast? Does it matter if the bark is interesting? What are the conditions (sun/type of soil/moisture level, pH...) the tree will be growing in?

Black gum (nyssa) is lovely, but grows really, really slowly. If you're young, you may live to see the tree achieve a decent size, otherwise, you're planting for future generations.

Eastern Rebud and Pagoda Dogwood are two of my favorite trees. Both have stunning form (I prefer single-stem on both counts) and the Redbud has breath-taking tiny pink flowers along its branches in the Spring.

Shagbark hickory would top my list for winter appeal. The shaggy bark does only come with age, however. Nuts are tasty too.

The shrubby red osier dogwoods have color appeal in winter.

We have 2 senior mulberry trees here. They are our "Halloween" trees with very craggy branches and shapes. The ones I have are not native but there is a native mulberry, Morus rubra that I would expect to be shaped similarly as a mature tree. Mulberry fruits are very tasty too!

Serviceberry and hawthorn (some species) are also native with pleasing shapes that flower and produce fruits. The hawthorn holds it fruit throughout the winter - adding to their appeal but take care of their 2" thorns. Serviceberries (aka juneberries, shadblow, saskatoons, etc.) produce a very tasty, early summer fruit but the plants can vary in habit. Some are more tree like, some more shrub like. Pruning can also help to direct that shaping.

FataMorgana

For a smaller tree, Sassafras albidum has a striking winter silhouette. Windy, interesting trunks and branches. Not to mention, interesting shaped leaves, aromatic foliage and stems, nice fall color, and host plant to very cool caterpillars of the Spicebush Swallowtail butterfly. However, it suckers a lot and will form a grove, which you might not want.

How about a nice little grouping of River or Paper Birch, which are beautiful in every season, especially against the snow in winter?

I agree that Cornus alternifolia, pagoda dogwood, has a beautiful form as it grows branches in horizontal layers. Mine bloomed and made fruits for the first time this year, and many birds enjoy the pretty blue berries.

For a large tree, American Beech and Yellowwood both have beautiful smooth grey bark when mature, and even when large seem to have delicate branches. However the drawback of a large tree is that it will be years before it reaches a mature form.

Whoops, I forgot to mention this tree should get at least 30' tall, and once it gets big, (and the roots get wide), about a 1/3 of them will be in a seasonally (springtime) swampy area. The native soil is clay, but about a 1/3 of the area where the roots will eventually reach is a nice, rich topsoil, as I've been top-dressing a wide shrub row with grass clippings, shredded paper, cardboard, and wood chips for 6 years now.
Interesting bark would be a nice plus, but the actual silhouette against the sky is more important to me. Rapid growth would only be important if it were REALLY rapid. How fast does an American Elm grow?
fatamorgana -- I have 2 red osier and a 'Winter King' hawthorn. I will check out the silhouettes of the shagbark Hickory and the mulberry. I like the idea of a craggy-branched, Halloween look.
Terrene -- I'll check out the Yellowwood and Sassafras, too. (The Beech will be too wide.)
Thanks, everyone. : )

Do search for Carpinus caroliniana; somehow I always forget about this tree! But it has an amazing and intriguing mature form, plus it has really cool, elephantine bark and the leaves are gorgeous Summer AND Fall.

Thanks, greenhaven. Will do.

I'm a fan of London Planetrees since native sycamores are apparently disease prone. They're relatively fast growing but ours fared better than most of our other trees in the record ice storm that we had in 07. They have peeling bark but not the "craggy branched Halloween look" like you mentioned. I think that kind of look would require some intentional creative pruning to get branches to grow at odd angles but I don't know what kind of trees that would work best on. Maybe the Bonsai forum would have some suggestions. We have a Japanese Maple between our house and sidewalk that I've had to prune a lot to keep in bounds and it's made the tree more interesting and very pretty. It's my Giant Bonsai. lol I know you're wanting something larger but perhaps it will work with another tree. Here's a thread in the Bonsai forum that has links.

Here is a link that might be useful: Yard Bonsai

Kelp,
Where (roughly) do you live? That would help a lot for making species recommendations.

Kelp,

Great question...and a lot of great responses. I just feel the need to "defend" the black gum. My father planted three of them in our front yard when I was a teenager. Once they became established, I thought they grew quite rapidly. I remember a picture of my sister beside the tree and in only about five years it was (relatively) huge. Now 20-30 years later I'd call them mature. They are not only beautiful in all seasons, they also provide berries for wildlife (at least the female ones do).

I also like beech in the winter, holding onto some of its leaves and backlit by the sun.

Also, if you I'd pick the American sycamore over the London plane tree--this is a native plant forum after all. :)

Nativeplanter -- I live in southeastern MA.