To be completely honest, if I had to choose between a roller coaster ride and another trip to the top of the Arch right now, I'd choose the Arch. It was that amazing to me.
More information can be found here. http://www.gatewayarch.com/Arch/index.aspx
If you plan on going, text the word Arch to 313131. You will receive a text for a buy one get one free admission to the top of the Arch. We took advantage of that.. our trip only ended up being $5 per person. It was a small price to pay for such an unforgettable experience.
The Arch Riverfront also offers helicopter tours, bicycle rentals, a museum, special exhibits, riverboat cruises, and documentary movies on the creation of the American West, the building of the Arch, and Lewis and Clark's journey. Not to mention the Historic Old Courthouse is right there on the riverfront.. Dred Scott, a slave, asked for his freedom at that courthouse.
I highly suggest that anyone who has not done the Gateway Arch experience DO IT when and if you get the chance. It's the experience of a lifetime.