When you've got yourself a fairly long slider (usually over 4ft.), it will often require one very very heavy tripod, or two simple lightweight stands. There's also a few sliders that ALWAYS require two stands, like JuicedLink's latest DIY slider. Rod's DIY solution is to use a single ironing board that is quick to setup, can adjust to various heights, fold flat, and is dirt cheap. [Thanks Rod] Keep note that you'll probably require some level ground as each corner is not adjustable.
If you're concerned about aesthetics, another cheap solution that mimics the same folding and height adjustment features as an ironing board is a musicians keyboard stand (as found below).