Because balcony space is limited in all but the most upscale apartments (and if you have one of those, you probably also have a country house somewhere, so this isn't for you), it's best to maximize vertical space to squeeze as much greenery as possible into your little outdoor retreat.
Enter the tower garden. Easy as pie, cute as a button, a single trip to the garden center and you can have this baby done in a single afternoon.
First you'll need a series of pots in decreasing size. It works easier if they're all the same shape, because they'll be nested inside one another - but feel free to get creative and use whatever pots float your boat. If you're feeling super creative, paint the pots to perfectly enhance your decor.
Your largest pot should be pretty large, as it gives the steady base - 24 inches or so. Successive pots can be the size you prefer - just a middle-sized and a tiny, maybe five pots of very slightly decreasing size. Remember that the space between the rim of the pot beneath and the bottom of the pot above is planting space, so don't make them fit too tightly.
Build a column of bricks from the bottom of the pot to about two inches from the top, then fill the space around the bricks with soil. The bricks provide a steady base for the next pot to rest on.
Place the next pot on the bricks, then add additional soil to fill the bottom pot to the desired height - the soil should cover a bit of the top pot's base for a more cohesive look. Repeat the process until your pots are all stacked.
Smaller pots may be too small for bricks so get creative. Smaller pots are lighter, so don't require as steady a base. Crushed soda cans work, or try an upside down coffee can.
If you're really wacky, you can forgo the support altogether and just let the smaller pots lean at different angles in the soil. Don't try this with the larger pots though, because the unsteadiness of it all could cause the whole thing to come tumbling down. You wouldn't want to be responsible for pedestrian deaths, now would you?
Keep the size and shape of the full-grown plant it mind - don't plant tall things where they could block sunlight from smaller, bushy things on the next level. The bottom pot is the best place for plants with deeper roots, while the tiny top pot may be best for succulents because of the unobstructed sunlight.