The Missouri Botanical Garden website has a searchable database that you can use to find plants to suit your conditions and needs. UConn also has a database for trees, shrubs, and vines that can give you some direction.

If you don't get suggestions here, try the Shrubs forum. I have never gardened in zone 4, so would have to look up any shrubs I might suggest.

I'm in zone 4 - and second the idea of taking a look at the shrubs forum - but I've got the Northern Lights azaleas (lots of images on Google) which were developed by the U of Minn. so are extremely cold hardy. They top out at @4-5'. Also have Althony Waterer spirea, Alpine Currant, "Dart's Gold" physocarpus, Mock Orange, Burning Bush, "Emerald Triumph" Viburnum (also Developed for the local climate), some kind of holly, potentilla, a few other things I'm forgetting, plus the usual range of evergreens - juniper, yew, mugo pines, Spruce, arbor vitae... Nothing but the evergreens have any winter interest, however, if that's a consideration for you.

Does the simply shaped green foliage of the lilac make a nice contast to the colored and cut foliage of your maple and smoke bush and so enhance their beauty? How about growing one of the smaller clematis that blooms later in the season over your lilac? (There is a gentleman, David5311 who sometimes visits the perennials forum who has successfully done this with multiple shrub/clematis pairings.) It will save you the trouble of starting over again with a new shrub. Get a big sized plant to start, not one of the little tiny starter plants so that it can compete with your already established shrubs, and match the ultimate size of the clematis with the ultimate size of your lilac. The folks in the clematis forum may have some specific suggestions for you. I know there are some clematis that are supposed to grow no longer that 5 or 6 feet (marketed as patio clematis, I believe), so they might work on your lilac.

Many shrubs don't have a long season of interest. Of Duluth's suggestions that I have grown, mock orange and burning bush are both of interest for a relatively short time period. Some of the northern lights azaleas have nice fall color and of course the gorgeous spring blooms, but not much summer or winter interest. Blueberries have spring flowers, summer berries, and fall color, and a few have nicely colored winter twigs. There are geen and white variegated red-twigged dogwoods which have the foliage during the growing season, spring flowers, summer berries, and the red branches in the winter. In order to keep it small enough it would need some trimming, but it is suggested that you prune about 1/3 of the branches down to near ground level each year to keep the branch color (older branches lose the bright red), so it might work for you. There are also veriegated euonymus with green and white or gold and white foliage. In addition to Anthony Waterer there are many other spireas that have green to gold foliage, pink or white blossoms, and some have nice red/gold/orange fall foliage. Some of the smaller weigelas have colored foliage, though their blossoming period isn't too long.

The Nishikii willow (salix integra 'Hakuro Nishiki') is pretty striking, and has interesting features throughout the year. It is listed as 4-6' wide and tall, but I have seen complaints that it can get much larger. Also supposed to be hardy to zone 4.

The pix in the link here are among the more striking I've seen. In particular, I haven't seen the bold red winter twig color in other photos.

Here is a link that might be useful: Nishiki willow pix

Ohh...how easy I forget about David's suggestion to use clematis. After reading a reference to this I planted an extra clematis at the base of a forsythia shrub. It is too early to tell how effective this will be (the clematis is flowering but it has not grown up to where the flowers are visible). I have been wondering about replacing a lilac that is growing in a prime location in my front yard, but maybe I will give the clematis idea another try!

Smoke bush and Japanese maple? Sounds like you could use something evergreen. A dark green yew might look good or maybe a yew that has hints of yellow foliage.

- Brent

i knew you would have excellent ideas! nhbabs, the idea of a clematis is a great one. i haven't seen this done before.
i will research options. brent in nova, i like the idea of a shaggy evergreen i have seen that is tinged with yellow. am drawing a complete blank on it's very common name!! doctorsteve, the nishiki willow is so lovely, but size a of mature plant worries me. i do love their color however.
i plan of planting myself in front of the bed this weekend and evaluate again with all of you input foremost in my mind! thank you!

A dwarf weeping Larch or a Gobosa blue spruce would add some winter interest.

I have a February Daphne (Daphne mezereum) that blooms very early and is totally covered with pink flowers. It fills the entire yard with it's sweet smell for about 3 to 4 weeks. It then produces green leaves and then red barries. It never gets past 4 feet tall and is slow growing. I like it because hardly anyone in this area has one so its unigue.

tyhawk, we love daphne's, but have tried twice (differnet house - different soil!) with no success. what zone are you, is the plant protected and is it full/partial sun?
great idea, thanks for the input!

Im zone 5 with a PH of 7 and its well protected with maybe 2 hours of sun. Good drainage.

Ditto growing a clem through the lilac.