I have grand plans for a swing set clubhouse adventure fort, but since other projects are taking so much of my time and budget right now, the kids will have to get by with an old-style tree swing.
The options were limited when we were kids: you swung on something hanging from a tree (the same place you got your climbing fix) or you had one of the metal tetanus risk swing-sets. You may disagree, but I think better memories were born from trees.
I built my swing with a rough-cut oak plank salvaged from a pallet and some poly-braid rope. I gave the edges a little rounding with a knife a some 110 grit paper, but I wanted the rustic look, so I didn't put too much time into it. I went with two holes per side in hopes of better stability and so that I could secure the rope back to itself with a couple of figure-eight knots. You can see how the knot is made here: figure eight knot.
The yard is still pretty swampy, so a full blown test of awesomeness has not been made. I think it'll work out pretty well... heck they have a blast jumping off couches and end tables, so its got to be at least that good.