I think most of us know this one as Schubert...

Noteworthy Characteristics: [from the web]

This chokecherry cultivar (sometimes called purpleleaf chokecherry) is a deciduous, suckering tree or shrub with a pyramidal habit which grows 20-30' tall. 'Schubert' is best known for its purple foliage: elliptic to obovate leaves (to 5" long) emerge green in spring, gradually maturing to dark purple by early summer. White flowers in racemes in spring give way in summer to clusters of reddish fruit (1/3" diameter cherries) which mature in fall to a dark purple. Fruit is very astringent, hence the common name. Fruit may be used in sauces, jellies and preserves, however. Fruits are attractive to wildlife.

Konrad

I would caution you about a Schubert or Canada red chokecherry due to their susceptibility to black gall. I have one in my yard (came with the house) and its infected--not bad yet but its in the main trunk so its just a matter of time...

Most of the Shuberts in the Winnipeg area are being decimated by black knot so I would advise you not to choose this tree. Very unfortunate as it is a lovely tree. We recently had a speaker from the City forestry department who said that they will be replacing all the Shuberts due to this fact. Many, many were planted throughout the city. How about something like a Japanese Tree Lilac, or Toba Hawthorne? I saw one of these last evening on a garden tour and it was lovely; little pink flowers that look like rose buds and no thorns.

Both above choices are good. I have a Japanese tree lilac and it's really taken off this year (3rd year).

Another good choice would be Thunderchild crabapple. If you do decide to get a crabapple DO NOT get 'Royalty' - it is very susceptible to fireblight.

Also, showy mountain ash.