Sargentina Crabapple
Any green-leaved Japanese Maple

It all depends what "small" means.

The tree forum might give you more useful suggestions. Cornus alternifolia is a favorite of mine.

nhbabs, thanks. I was just thinking I should perhaps put this question in the "tree" forum.

plantman314! I was just looking at the japanese maple! I am afraid that a southern exposure might be too much for it.

Thanks for your responses! This was my first time posting!! Thanks again!!

Partly why My favorite tree is my favorite is because it grows so well in my climate zone. I have no idea what would do well in your zone, a much colder climate. This is when I take my questions to the local nurseries, they know what grows best in that area because they'll be left with the cost of a tree if they have to honor a one year warranty. If a customer returns complaining they did everything right but plant died anyway now the nursery has to eat the cost. So it's in their best interest to carry only those plants that can survive in that region. This is why I only buy gardening books that specify West or California. Anyway, I'll answer the question but keep in mind this tree is recommended for zone 9 none zone 5. And I'm not a professional designer,etc so this is just my opinion based on what does well in my garden.

My pick is the Crape Mrytl. I have one in my front yard next to the driveway that I planted over 10 years ago and it's still a very,very small tree that is drought tolerant, puts out a beautiful display of flowers, doesn't tear up concrete around it nor drop nasty seed pods,etc on the ground. So for me, it was the perfect all-around small tree. You didn't specify evergreen or deciduous, you might want to decide if that matters. This one is deciduous.

Dwarf trees have done very well in my tiny garden. I have a dwarf weeping cherry that has grown in a planter box for a decade and is still as tall (3'?) as the day I planted it and not that much wider.

Small trees in my yard can mean 3' or 10', depends on what you mean when you say small tree...do you have a height in mind?

I planted a star magnolia in full sun (southern exposure) in Chicago (z5). It did very well.

a few suggestions:
serviceberry
red maple
star magnolia (in a protected spot)
flowering crabs
Chanticleer pear
cornelian cherry (a type of dogwood)
flowering plum
redbud

The Chicago Botanic Gardens website has info on the flowering crab cultivars that do well in Illinois.

Rachel

I love flowering crabs...AND japanese maples. I'm not sure how a JM would do up there--with that exposure--but a good local nursery would. Acer dissectum 'Viridis' and 'Waterfall' are both good greens to consider--though they stay small (10 feet at maturity.)

Star Magnolia did well at my mother's zone 5 house in NE Ohio. I'm not certain what variety--I didn't bother learning cultivar names until after I had my own garden and by then my mom had moved.

melanie

is a bloodgood, which is hardy to zone 5B. But it is in a protected spot.
Rachel