Cranberries are inexpensive and can be purchased at your local grocery store during the weekly run, no special trips to a craft store for these ideas (well ok, maybe one trip).
Now that I live in an apartment building I can't make this wreath, but it is one of my favorite things to make right after Thanksgiving. Its super easy, very inexpensive, and looks great when you're done! Just get a styrofoam wreath (square or circle), paint it red, and go to town poking toothpicks into cranberries and then poke into the wreath till its all filled up.
Another cranberry wreath idea comes from Martha Stewart. String cranberries and then wrap around a simple wreath, use with or without a bow and it looks great!
I also love this idea for all over the house. Just put some cranberries at the bottom of a glass vase, and instant chic Christmas decor! Great for flowers, candles, or branches like below.
Cranberries float in water, so using them with some floating candles. Also works well with vodka, in one of those decanters...add a few whole limes in there and you have instant red and green decor in your booze too :)
And last but not least, the very traditional popcorn and cranberry stringing. Can be used many places other than just the tree. Try wrapping around your stairs (do this one if you have no carpets on the stairs, cranberry stains are not fun), drape on a mantle, or drape over a hall mirror to create a welcoming look in the front hall.
Pictures from marthastewart.com, hgtv, whitelacewedding.com, thisnext.com, bemisfarmsnursery.com, and flickr