I like things that leave a definite, final 'image'. For example, you might have four aces on the table and a spread-out blank deck, or three cups with three lemons on top. In other words, something you could take a photograph of and it would pretty much sum up the whole trick.
Currently my favourite closer is something I devised myself called 'Christ on Bike' (based on Henry Christ's 'Tally-ho'). It's nice because, whilst it is quite long routine, there is a lot of spectator involvement and the final 'image' you create in the routine looks really good and memorable, and you can (if you want) just get up and walk away from it. I don't really want to describe what it is as I don't want other's copying it...sorry!
Not sure at all if any of that makes sense, but hopefully I got my point across.
Rev