There's a newer Hampton Inn with a Krieger's just off 40/64 pretty much smack in the middle of the zoo/science center. 10 minutes tops to downtown.
Hampton Suite Stl Forest Park
5650 Oakland Ave
Saint Louis, MO 63110 US
Don't have a phone number - sorry.
There are also a few in/very close to Union Station. That's a place where if you don't mind a 8 block hike, you can actually walk to the arch, baseball stadium, etc. You're 10 minutes to the zoo and science center. Down there, you can also jump the metro to the arch or down to LeClede's Landing which has tons of shops, eats, clubs, etc.
Bryan