Gateway Arch, Forest Park Museums, Zoo, Saint Louis Cathedral (world's largest mosaic) Dog Museum (in a nearby town, off the beaten path, but interesting), Video Game Museum (it was downtown, not sure if it's still around).

We live several hours north of St. Louis, and it's a great weekend destination. I'd add a few attractions to the ones listed above -- if kids are involved, a trip to the Science Center will have them enthralled for hours. The Botanical gardens are beautiful and easy to get to. There's a geodesic dome with a rain forest inside, lovely trails through a Japanes garden, and other gardens. The courthouse right near the Arch was the site of the infamous Dred Scott decision and has quite a nice display. The zoo is really nice, again more for kids, but it's in the Forest Park area which itself is a nice destination. Across the river in Illinois about 10 miles or so are the Cahokia mounds, which has a fantastic museum on these early Indians. Plus you can climb the mounds and get a nice view of the city/Arch in the distance. The museum under the Arch is a very interesting frontier museum with lots of nice displays and excerpts from lewis and Clark, I think. Without doubt, our favorite restaurants are in the Hill area, the Italian neighborhood. Zias is the one we always go to, long waits if you get there after 7, but it's large and worth the wait. Our three favorite hotels are the Adams Mark (right across from the Arch, very nice public space, rooms are ok); Marriott (good location, usually has good weekend deals, right across from Busch stadium if you want to see a baseball game, which by the way, has an interesting museum in it too if anyone in your group likes baseball or wants to tour the stadium). Union Station has a Hyatt, I think, it's huge,the rooms are nothng special, but it's right in the station, which has been converted to a shopping mall with not so great shops. But the old train station rooms are really nice. All in all, it's a very nice city.

If you're looking for nighttime entertainment, try the Fox Theater (www.fabulousfox.com) It's a beautifully restored theater, gets lots of broadway touring groups, concerts, etc. Good parking and easy to get to.

It would help to know your interests and the make up of your group. I think you have some great information in the above messages. I would add that the new City Museum is a great place with or without kids, there is an enormous 4th of July celebration called Fair St. Louis which takes over the whole downtown area by the Arch,and there are a variety of fun places to eat by the river front in an area called Lacledes Landing (including Planet Hollywood).I would be happy to give some restaurant recommendations if you could give a little information about your requirements. Have fun. St. Louis is a great place to visit but if you come here in the summer expect heat and humidity.

Ditto about staying at the Marriott downtown if you want to see the Cardinals - it took us about 7 minutes from our room to our seat in the ballpark and we never moved our car - we've done that twice and thoroughly enjoyed it. Another nice area is St. Charles, west of the airport. The downtown is full of antique shops and nice stores. Grant's Farm was fun for my kids years ago and at that time the animal shows (chimpanzees, elephants, lions, seals)couldn't be beat - these shows were at the zoo not Grant's Farm. We enjoyed Spaghetti Factory in Laclede's Landing and the restaurants at Union Station - drove by Scott Joplin's birthplace. If you're lucky you'll get a room with a view of the Arch, which is beautiful at night.

All of the above messages are very good. There is one thing that I would definitely not waste my time on. DON'T waste your time going up in the St. Louis Arch. It is not worth it. We took an all day tour of the city that was excellent. We saw the botanical gardens, The Cathedral ( absolutely awesome ), Union Station, downtown and many other interesting sites. Strongly recommend the tour if you are not familiar with the city.

I think the Arch area is the best place to visitand you really must go to the top of the Arch. It's a very uniques experience just sitting in the eggshape elevators that have to arch their way to the top.

Aside from the above postings, there are a few "locals" attractions that may be worthwhile. I like to think of St. Louis as the Las Vegas of the mid-west (forgive me Tunica, MS). Casinos are abound...just follow the billboards. Sunday brunch at either the Chesire Inn or the Regal Riverfront are recommended. Personally, the Regal is where it's at. Situated a top their hotel, the dining area is revolving, so you'll be sure to catch a glimpse of the surroundings. The brunch is the best I've ever head (e.g. smoked salmon, chilled jumbo shrimp, etc...). If possible, try a ballgame at Busch stadiums. Newly rennovated, it's a treat for you as well as the kids. The Bowling Hall of Fame is nearby if your interested. A tour of the Anhieswer-Bush brewery is a great draw.
Historic downtown St. Charles, a few miles west of St. Louis, is a great way to spend a few hours during the afternoon.
Can't misses include Forest Park and the Fox.