There's a cute area called De Mun, which is a block or so off Clayton Road near Skinker, next to the Concordia seminary, next door to Wash U. "Jimmy's" is a restaurant there I enjoyed last August. There's also a good coffee shop on the corner, for mornings.
If you like Italian food, you can't beat the restaurants on "the hill" in St. Louis. In fact, I know there was a thread here recently devoted to the best food there.
Congrats on having a son at Wash U.! It's a great school and not easy to get in to.

The central west end has Bar Italia - it has fantastic menu, wonderful outdoor patio, etc,.
Cafe Zoe - great pan asian -nice atmosphere
Cafe Eau - in the Chase Park Plaza hotel - fabulous food, great bar, wonderful live entertainment( the place to go to see and be seen!)
Duff's - wonderful upscale bistro type restaurant.

If youare staying in Clayton - there a great places there too.
Remy's
Cafe Napoli - great wine selection, great food, a little jazz bar attached too.
There is a intimate french bistro in clayton, I can't remember the name, but I will and post back. It si on Wydown Ave.
An area called the Loop - your son will know where this is - there is a new place called 609. GREAT food - sort of a pan asian influence.

Enjoy your stay? Is it Parent's Weekend?

There are many good places in the CWE, Clayton and Downtown.

Clayton:
Barcelona: tapas place that recently expanded. Very good sangria.
Portabella: Italian influence. Can be expensive.
J Bucks: even though a celebrity themed place I've always enjoyed eating there. However if the Cards are still playing skip it, the place will be a zoo.
Miso: Japanese/sushi place.
Harvest: book now if trying to dine on the weekend. One of the best places to eat in St. Louis.
Jimmy's Cafe: just down the street from me. I need to go there more often.

Maplewood (5 minutes south of Wash. U.):
Monarch: hottest new restaurant in St. Louis.

Central West End:
Cafe Eau: excellent. Place is subdued so if taking a group might not be the best bet.
Balabans: a CWE mainstay. I've been going there for 20+ years and have always had great meals.
Liluma: never been there myself but always looks busy and friends have been pleased.

Downtown and nearby:
An American Place: just opened in the Renaissance. Supposedly same owner has places in Chicago and NY that are great.
1111 Mississippi: in the Lafayette Square neighborhood. Excellent.
King Louies: not in the best neighborhood but wonderful food. Every time I've been there I've seen one or more VIPs.
Sidney Street Cafe: my favorite place to eat in St. Louis.
Top of the Riverfront: food is pretty good. Expensive but the view is worth it.

I have heard a lot of good things about Monarch, haven't been there yet. We love Sydney Street as well and Soulard Restaurant is one of our favorites because it is good food, but you can be very casual. We also love Modesto on the hill for tapas. I like Remys as well. I have never been that big of a fan of Balabans although I have been there for all three meals at various times!

My son and daughter-in-law used to live in Central West End and I agree with the other posters that it's got really great restaurants.

Having said that, my most memorable meal in St. Louis was downtown at Tony's. That was back in the days it was a 5* restaurant. Is it still good? I'm afraid I read somewhere that the quality isn't what it used to be.