Depending on the size of your yard you can get a cheap frisbee golf basket on a portable base and a few putters for a ton of fun. If you have the right shaped yard and a couple of natural obstacles (like, um, houses or trees) you are good to go.
Avoid the crappy foldable ones (like this:
http://www.discgolfassoc.com/phmachlite.html)
and go with an M-14 (
http://www.discgolfassoc.com/phm14.html )
For discs you can just grab a bunch of Aviar putters (
http://www.dtworld.com/Aviar_Putter_p/g42-dxp.htm ). Get some of the lightweight ones for kids and a few heavier for adults.