While tooling around last weekend, this caught our eye: free coffee grounds being unloaded by the Starbucks on Lindbergh in Hazlewood, aimed specifically at gardeners. We're not sure if other Starbucks do this, too (but it's worth a call to the one you frequent) and if you eschew Starbucks, it's worth asking your friendly neighborhood coffeeshop to see if they, too, have excess grounds they would like to get rid of.
And of course, if you drink coffee at home - ground are 1.45% nitrogen, and can be mixed directly into your soil - it's still worth saving your own.
There's a lot of other free stuff floating around out there, actually, that's useful for gardeners. Schlafly leaves barley sacks (sometimes plastic, but usually thick brown paper) near the newspaper racks at both Tap Room and Bottleworks; they make great weed barriers/paper mulch. If you have a chicken coop, coffee chaff (again, ask your local coffee shop about this) makes great bedding for birds. They are also pretty wild about spent grain, a by-product of brewing (and lord knows there's no shortage of microbreweries, or macro-breweries, in St. Louis).
Dear readers, do you know of any other resources like this? What have we missed?