Whether your garden area is 10 square feet or 1000, chances are there's more you'd like to plant than you have room for. This Instructable will give you tips to increase your growing capacity without spending a lot of money.
Step 1: Grow UP!
Plant squash, bean and cucumber varieties that vine (not bush varieties). Plant these on a trellis (in the case of cukes and squashes) or, in the case of pole beans, up a bean teepee. A teepee can be made of any long, slender poles (I used furring strips I found in my garage, and tied them together with zip strips). For pole beans, the teepee should be at least 5' tall. You can use fencing as a trellis as well, whether it's chain link, chicken wire, welder wire, or whatever you have. Plants might need a little guidance to know where to grow, just be sure to treat them gently so you don't break the stems.
Step 2: Grow up with a potato tower
One space-saving way to grow potatoes is with a potato tower. Here's how it works:
Make a tube of fencing (as seen below), or out of a trash can with the bottom cut off. Plant your potatoes as you would normally, but more densely (5-10, depending on diameter) in an area the size of your tube. As your potatoes grow, add alternating layers of straw and compost, leaving about 6" of leaves exposed at all times. At the end of the growing season, when the plant leaves start to die back, you can kick over the tower and pull out your harvest of potatoes.