I strongly recommend a Cornus kousa of some kind. Has showy "flowers" in late spring, then showy berries in late summer (which are actually delicious to eat) and good autumn colour. Though nothing special in mid-winter.

I'm fond of my snake-bark maple. I think the bog-standard Acer davidii are not the best. I have Acer (grosseri var.) hersii (sometimes considered a subspecies of Acer davidii). Hers's Maple, which does what the previous poster says, and has showier snake markings than some. But they do fade a bit in the winter. Acer pensylvanicum is another one with very showy stripes. Other bark-trees that can be considered include the paper-bark maple acer griseum, and many showier birches, though some of those can get a bit big. Unfortunately Arbutus x andrachnoides gets very big.

I find my amelanchiers a bit disappointing. Flowers for 10 minutes, berries not so wonderful unless you choose the variety carefully, and does need a moist non-alkaline soil to grow well.

I rather like kowhai trees, which are some NZ sophoras such as microphylla and tetraptera, and there are also some "improved" garden cultivars. They have tiny evergreen or near evergreen elegant mimosa-like leaves, which provides year-round interest, plus yellow flowers in early spring, and long seed-pods. Though need protection from cold winds.

There are of course many coniferous evergreens. Choose your own favourite.