Timmy,
I wish I knew which shows are worth seeing there these days, but I would definitely check out the websites for Second City, IO, and the Annoyance Theatre to see what's showing. I can say without reservation, though, that if you have the chance to see "T.J. and Dave" at IO, definitely see it. Maybe you've already seen them, though?
If you're near Michigan Avenue (near the Wrigley Building), I would recommend stopping below street level at The Billy Goat Tavern. I always have one of their "cheez-buggahs" when I'm back in town. They're horrible for my arteries but great for my soul.
If there are any good bands playing at Cabaret Metro on Clark Street, you might want to stop in there, too. It's still my all-time favorite place to see live music.
If you're near Second City, and you feel like having a beer or twelve, you might want to stop in at The Old Town Ale House on North Avenue across from the Second City ETC space. It's worth it just to see the old painting of Del Close (and others) on the wall.
I wish I knew more about what's happening in Chicago these days. You could always check out the Chicago Reader on-line or New City on-line for more info.
Have a good trip, sir!
Brian