Look for something with decorative bark, for winter interest. Somebody mentioned Coral Bark Maple; another interesting maple is Snake-Bark Maple.
Look for interesting shapes, as well. There is a dwarf Black Locust "Twisty Baby" that has an interesting shape, interesting bark, and white flowers in spring. However, the Black Locust species (Robinia psuedaccacia) has some bad habits (brittle limbs and prolific suckering); I don't know if the dwarf cultivar has overcome those. Harry Lauder's Walking Stick (Corylus avellana "Contorta") has an interesting shape year round. Hammelis (Witch Hazel) blooms in winter with yellow or coppery orange flowers, and has an interesting shape year round. There are some Japanese Maples that have fabulous shapes.
Barb and the Two Furry Speedbumps