They are similar but Norway maple leaves tend to be a bit wider than long (or at least in appearance), and they have almost a rectangular shaped leaf overall. They also tend to be a bit larger than a sugar maple leaf.

Sugar maple leaves are approximately the same width as length. Overall they have an equilateral pentagon shaped leaf. If you were to draw a line from lobe tip to lobe tip you would see what I mean by rectangular or pentagon. It is difficult to describe, but if you search through some images you should be able to see what I mean.

Maybe the attached link will help. If you click on the thumbnails of the photos, you'll get close ups. I agree with Matt that differences are hard to describe - a picture is worth a thousand words :-)

Here is a link that might be useful: maple leaf identification

I'm sure Red Maples are common planted trees in Chicago area, they are so commonly used in the Midwest now. Bigger Red Maples have uglier different bark than Sugar Maples, but younger trees just have smooth grey bark.

Your gonna see a lot of hybrid maples Acer freemanii cultivars as street trees in the Chicago area, Autumn Blaze being very popular. More Norways than sugar also since these take pollution better than sugar, then also a lot of silver maples and also the red maples. Maples are a very popular street tree in the area. I would guess 2nd only to ash trees in their usage here.

Bill

Snap off a leaf, or this time of year, a small branch. If you see a milky exudate, it's norway. Number of lobes on the leaf (norways have more) and shape of buds (sharp=sugar) are also ways to tell, but you're going to have a guide to start with if you really want to understand the differences.

What other trees are used as street trees? Start naming them, yep, it's used. The most common Acer species are going to be A. saccharum and cultivars (I'll include some of the less common forms and sub-species here), A. rubrum and cultivars, A. x freemanii and cultivars, and I'm willing to bet there are still going to to be a lot of A. saccharinum
around. Less common are going to be the smaller growing trees, A. griseum, A. triflorum, A. ginnala. You may even see a few A. negundo, as unappetizing as that sounds, but in the end, if it's conceivable it could be grown in the area, there's going to be a few of them arouund.

Some of the best street trees (Eucommia ulmoides, Corylus colurna) are rarely used because of recognition factors, and many are overused because of recognition factors (Acer). Visit a few local nurseries or contact the forestry department. If you life in a suburb, check with that town/municipality as well as some of the specifics may change with the jurisdiction.