Wreaths are a very popular Fall/Winter decoration and are easy to make yourself.  There are plenty of alternatives to using store bought items or a lot of plastic, here are just a few ideas!
Acorn mirror by Martha Stewart
Buy a secondhand mirror or use one you already have and simply glue acorns to the surface.
Harvest Wreath by Martha Stewart
This wreath is made using leftover corn husks! So, start saving them now. 🙂
Moss Wreath by Instructables.com
Start with a foam base and simply glue on your moss!
Despite using re-usable shopping bags, I still have a ton of plastic bags; this project will use them in a very creative way! You also need wire hangers and pliers. Find another version here.
Of course, you can always buy an organic wreath like the one below from 
Yes, those flowers are made out coffee filters! How creative is that?
A great way to use those old greeting cards you have!
Tips: Try using organic glue, make a very easy wreath circle out of cable wire, soak branches in mulling spices before using them for a scented wreath, try adding black and white photographs like in the Pottery Barn one below to your wreath, see what you have in your home (recycling bin, craft boxes etc) before heading to the store and remember that styrofoam can be recycled!