The "make it your own" thread had me thinking. Then at lunchtime I heard Elvis Costello on the radio doing a live piano+acoustic medley of "Alison" and "Tears of a Clown" (cool idea, not so terrific execution), which got me thinking further...
Sometimes the 'surprise' of a medley can be really effective, when one song morphs into another. Hard to think of an example where the whole is better than the sum of the parts, but: anybody got a 2 or 3 song medley that just works? You know... slays 'em?