Cereus peruvianus monstrosus|
I water this during it's growing season, with just the occasional splash in winter.
Put it in a small pot with good light and an infrequent half-cup of water, and forget about it.
This form doesn't seem to like to flower, but all of mine tend to get potted and put aside for show; I think, don't quote me on this, that it and it's regular form doesn't like to flower unless it has room for its roots to spread out.
I've seen much bigger plants than this one that are all blue. This one is over 15 years old as of 2008 and has always been in small pots and kind of neglected. Those are tree seeds on it, which gives you an idea of how much I neglect it.