I just made three postcards for the Green Postcard Challenge.
Go check out what everyone else made, there are some really cool recycled materials being used.
Mine are pretty conventional and are made with:
fabric scraps that most normal people throw away
rescued/recycled upholstery fabric
painted batting leftovers
a green ribbon from an Amazon.com gift
a mesh plastic bag that used to have limes (it melted on the postcard above, you can see the remnants as a very cool grid-ish pattern on the left side)
all on fusible batting scraps.