Inspired by the reactionary car-gardeners of Amsterdam and an eponymous book I saw in a local bookstore, I undertook, a couple of years ago, to beautify my rather bleak urban environment by planting a tree on the thord-floor breezeway of my apartment complex. In the spirit of the book, I wanted to do so without spending any money. Soil and plants are easily had for free, but the container presented something of a challenge. At least until I saw the discarded commercial clothes dryer in the back alley. I set to with a crowbar, and in no time I had liberated the machine's drying bin which, knocked on its back, makes a great planter. The steel has been enamelled an attractive blue color to resist corrosion from wet clothes (or wet soil), and the vent holes in the back/bottom find new life as drain holes in the reincarnated planter.
I hauled the bin up two flights of stairs and set it up in a sunny corner of the breezeway. Then I brought up a bucket of river stones and put a 6" layer thereof in the bottom, and filled the rest up with soil, and put a nice decorative layer of pea gravel (all freely "harvested") on top. I did this gradually over the course of a month or two, one bucket at a time, as was convenient. Then, as often happens, the project was put aside for a few...er, months, while I worked on other, newer and hence more interestig ideas. And then, one summer day, when I came home, the planter was gone. As angry as I was with my apartment complex's maintence staff, I have to give them props: Filled with dirt and rocks, the thing must've weighed 300 lbs. I never thought they'd even try to move it.
Here's another commonly-found freebie item, recycled as a small planter for an urban setting. Just turn the cinder-block with the holes positioned vertically, put a layer of gravel in the bottom, fill with dirt and plant. You could seal the bottoms with concrete if you wanted to make this more permanent and easily movable, or you could just slide a cookie-sheet under the thing when you want to move it. Much will depend on the ground surface in the location you want to use it.