Tough spot.

Redbuds here seem appropriate. They'll need pruned.

In St Louis people plant many of the red maple cultivars there.

Oh! Nyssa sylvatica (we call it black gum here). Over in Florissant there are a few doing curbside duty in 50/60 year old neighborhoods looking well. Nyssa probably will grow the next size larger than your Pears but they'rea very polite tree far as not making undue messes. Excellent fall color. Also looks in the pictures like you have some of the larger Callery pears I have seen.

I second Nyssa sylvatica! One of the most beautiful trees on earth. It is sometimes called tupelo here in GA, but also blackgum too occassionally. I am in mostly shade and my two have great color, yellows to oranges to reds, often on the same leaf.

Yellowwood is also a great choice. Sassafras is good too, but I caution you that they are very slow growing and hard to find in the nursery trade. (At least they are hard to find in my area.)

Kentucky coffeetree would be a great selection as well.

If you are thinking oaks, I would recommend White Oak, Shumard Oak, Wilkow Oak, and Swamp White Oak in that order (swamp oak may also be known as Overcup Oak/Nutall Oak? They may or may not be all the same species). I have an Overcup Oak which has a great shape and it has pretty yellow/orange leaves in the fall. Tolerates a lot of water.

Stay away from these: sweet gum (raises sidewalks), silver maple (branches are weak and break off in storms), pin oak (the bottom set of branches always droop downeven if trimmed, so it can be a pain the the ass to maintain.)

Here is a link you may find helpful:

http://www.kentucky.com/living/home-garden/article44419065.html

Also, my vote would be for you to remove the pear trees, grind the strumps, and replace with the new trees. Those pears may compete greatly for water, so it may take longer than you think for a new tree to establish there. (The pear's root system may also be taking up a lot of room in the growing space there.) They also appear to be perfectly located for the “new/better" trees that you want to plant. Just make sure you get any permit needed if you are within a city limits and they require it.

Maybe you could replace one tree with a 2-3" caliper tree, then wait a few years and replace the other tree, so that your shaded yard can adjust over time?

Awesome user name, by the way!

Either would be a decent choice. Yellowood's big weakness is it has bad
crotch angles that make it vulnerable to wind. Is that likely to be an
issue there? Slightly bigger then callery pear. Sassafras is hard to
find and hard to get established, but would work great and give you good
Fall color if you got it established in the first place. Redbud are smaller and short lived but pretty and easy to find. Honeylocust tend to do well in those Hell strips.

Are power lines an issue? What killed the Callery Pear?

Thanks for the replies. Someone in my neighborhood suggested Nyssa sylvatica and I had forgotten that. I definitely want something more polite than the Calleries. And for some reason, I didn't think about the new trees competing with the old tree - thanks for pointing that out. We had discussed taking one out this year and the other a few years later, so we'll probably go that way. As for position, we'll probably need to shift one of the new trees inside a bit as there is a fairly large, old Hawthorn further back in the yard that needs a little more room.

These trees are some of the larger pear tree that I've seen. I don't know what is knocking them back, but they were planted in the early '90s by the previous owner, so old age is probably a contributing factor. Power lines are on the other side of the street, so no direct issue with them.