I wouldn't do the aspen (or poplar, or "popple" as a lot of people call them where I live) - fast growing, yes, but very short lived, branches break off, etc. Made the mistake of planting a couple of "hybrid poplar" some years back and recently cut them down... One of the nicest trees I've planted from a seedling is a "Sunburst Locust." Slower growing, but I love the form and the leaves are tiny and easily mulched up or collected with the lawnmower. Definitely agree with Rick about the ash trees, what a bummer but they will probably go the way of the elm trees. Why not consider some fruit trees for a double-duty planting? I also like the river birch, we have some on our property and, while not white, they have very attractive bark.
