Here a suggestion for a small flowering tree to plant along a boulevard, a Japanese lilac tree (Syringa reticulata). While bigger than lilac bushes, these trees are small, usually no more than 20-25 feet tall, and slow growing, so buy the biggest one you can afford. They bloom later than "standard" lilacs, late spring and early summer. In particular the plumey affect of the inflorescences as they transition from green to creamy white is very handsome. On our campus they make nice landscape trees between buildings and sidewalks, and because they are a convenient size, they seldom out grow their spaces, or not quickly at any rate. The flowers are quite fragrant, but a bit muskier than standard lilacs. This is a great tree to plant when you've grown tired of flowering crabs and Bradford pears.