I don't live there anymore, but check out the school for the blind (it's off grand, i think) it's a nice ledge spot in an alley and the bust factor is nil, plus you'll run into plenty of skateboarders there. The post office by SLU is a weird/nice ledge spot. Keiner Plaza downtown (although I haven't skated it in a couple years, it still might be good... they drain the fountain near fall and dudes shred it) Check out the Jefferson Barracks park, and if you're ever desperate in the winter there is rampriders or the plan 9 park (both are indoor and lots of BMXers) it sucks but if you're eager in the winter to skate, its better than nothing I guess. St. Charles has a fun outdoor park if you make it out that way ever.
Infinity Skateshop
5528 South Lindbergh Boulevard
Saint Louis, MO 63123-6956
(314) 843-1989
...is pretty much the only legit shop in that area hang out there and you might be able to link up with some folk... do you not have a car? if not' check the bus schedules and metro-link schedules... to be honest, I hated St. Louis it's spread out and you need a car when you live there otherwise you're kind of fucked. Plus the skateboard scene is really cliquey, I think that's changing thanks to shitside and dude's building shit.
http://prettyskateboards.blogspot.com/ a local dude's blog/company or art project? ...some of these guys are cool, some of them are total fuckwits. but it's all whatever. they are friends with Randy Ploesser and think they're overly cool at times, blah blah.
Hope this helps, and good luck dude.