Illinois is worth keeping in the Union for Shedd's Aquarium. Oh yeah, and the US needs a couple of states to form the bottom end of all of the statistical bell curves, so Illinois has been good for that function.
You would have to come for a crosstown rival game, Cubs vs. Soxs. I would recommend going when it it is at Wrigley. It is a more enjoyable experience and the Sox's fans are more behaved when there aren't as many of them.
Wow so glad to hear that so many of our fellow Illiniosans enjoy our state so much...ummm MAYBE that's why we have some of this issues we have because our people just don't care (not that I'm specifically saying that any of you are those people). Anyways, adressing the question at hand; Galena is wonderful especially in the fall and spring; Southern Illinois is great especially if you visit in the winter because it's not quite as cold as up north- If you like vineyards or would like to experience them, there are more than a couple dozen just south of I-64; and the given that everyone talks about is Chicago. I personally don't care for Chicago (it's just too big and crowded for my taste), however, there are several things to be seen in Chicago from a tourist's point of view. Those that have already been stated are great (I'm a Cards fan too but you just have to appreciate Wrigley Field) plus there is Shed Aquarium, Navy Pier (which is at Lake Michigan), museums, etc. Illinois is a great place to live and visit even though it may not have the glam that some states have with the ocean or mountains.
If you're coming in the fall, Illinois has some of the prettiest colors I've ever seen. The weather can be unpredictable, so that could be a concern, but it's well worth it. There are a lot of great places to go mudding because there's really not much sand or rock up here. Chicago is, of course, a big tourist attraction, but I personally think it's a little crowded. Galena is nice, and so are all the little towns you can find just driving through. Nauvoo is great if you like historical little towns.