I like to sew recycled clothing- it's cheap, low-pressure sewing. As far as I can figure, you either make something cool or you get rid of some clothes you never wore anyway!
This is a recycled-t-shirt skirt I made for a friend. It's a tiered, patchwork skirt. The pattern is adjustable for however much fabric you have (within certain minimums).
Step 1: Harvest Fabric
This skirt used 6-7 women's t-shirts. I only used the parts that were solid colors. Your needs will depend on the size, cut, and style of the shirts, and the skirt you hope to produce.
Cut them all into rectangles. Mine were mostly six inch squares, but you can introduce some variation in width as long as the height of each rectangle is the same.
Step 2: Lay It Out
Figure out how you want your pieces to go together.
The important thing here is that the top piece is about the size of your waist (so if you have a 25" waist, your top row should be 25" across). You will lose some fabric to seams, but that's good because the fabric is stretchy and it will make a secure waistband.
The other important point is that the width of rows should increase as you approach the hem of the skirt.
In the picture, the right side is the top of the skirt and the left will be the hem.
Step 3: Sew It Together
Sew the tiers into long strips, then close the loop for each one. You should have a bunch of fabric circles of different sizes.
Step 4: Gather and Sew
Sew a basting stitch (as long as your sewing machine will let you) around the top of each fabric circle (except the top one, which will be on your waist). Pull on the top thread to gather until the fabric is the same size as the fabric above it. Sew together.
Step 5: Make the Waistband
Double over the waistband to the inside of the skirt (see pictures). The edge of the top row should just cover the first gathered seam. Sew.