If it has a strong vanilla-type scent and is growing in a moist area, check out swamp azalea, Rhododendron viscosum which occurs in white most commonly, but also in pink.

Joe - Nah. Not an Amelanchier. Foliage is not quite right, and Amelanchier flowers have skinner petals. Carol - that could be it. Definitely something in the Rosaceae family, I think. My only hesitation is that this garden was neglected for quite some time, is overrun with lonicera (both vines and shrubs), berberis, Euonymus alatus, etc. And these shrubs are covering an entire side of the suburban yard. It looks like they've been there for a while, and they're taking over along with the rest. Has P. villosa been around for a while? Does it show invasive tendencies here?

Dwarf conifers are a possibility - there are scads of varieties and many will never exceed 15' in a lifetime. Since they are evergreen, they look as good in winter as in summer, but they don't flower and they don't grow fast. Evergreen flowering shrubs are limited for your hardiness zone but you could look at rhododendrons or pieris. Some varieties are more sun tolerant than others but again, none growth particularly fast. There are any number of deciduous flowering shrubs that could work for you - lilac, forsythia, smokebush, rose of Sharon, chionanthus. These tend to grow more rapidly than either conifers or broadleaved evergreen shrubs but they are pretty much uniformly naked in winter :-) It is hard to find any flowering trees that wil remain below 15'....and even these generally tend to have naked trunks or seldom branch to the ground. Personally, I would opt to create a larger planting bed somewhere along the street side that is appropriate to your screening requirements. And I'd use a mix of plants - something tall and full to provide screening, something that provides seasonal bloom color and something to give evergreen/winter attraction. I know not everyone thinks this way but a tree (or two) or even a large shrub plunked down in the middle of the lawn looks to me extremely awkward and disconnected. Even less appropriate with a small garden such as yours - it comes across as a bit of an after thought instead of a planned landscape. I would much prefer to see a well thought out planting bed with maybe a larger tree to anchor it and smaller shrubs as an accompaniment.

Here is the winterberry from my upper garden (where I know that's what it is -- it was purchased from a nursery years ago): the leaves are glossier and have a more definite point at the tip, but otherwise, I do think both are winterberries! (Wonderful news!)