I've always wanted a tree swing, but have never lived in a place that had a tree strong enough to support one. If you're lucky enough to have a nice, sturdy tree near you, and are willing to let me stop by for spontaneous swinging sessions*, here's a great tutorial for making a tree swing that'll last!
To start, you'll need to get your hands on some 2x4x8 lumber and a some heavy duty rope. Once you've got those, check out A Beautiful Mess for the full supply list and tutorial!
*Not required, but highly recommended. Plus, I'll bring you cookies.