Endings

We, the Editors, are studying the hold-for-voting stories for the new May 31, 2012 ElectricSpec Issue. There are a lot of good stories there. (Thanks for submitting if you did so!) One major key to a good short story is the ending. And, apparently, it can be difficult to write an excellent ending.

A story ending has to do a lot of things. A good story ending is both a surprise and totally obvious. It's a surprise in that the reader cannot predict it, but it's obvious in that it fits in perfectly with what has gone before. Often, a good ending makes readers rethink the entire story; it causes a kind of paradigm shift. A good ending needs to address both the external plot arc and the internal character arc. (I've got a tip related to this: can you summarize your external plot arc in one sentence? How about your internal arc? If not, your story may be a bit muddled.)
Most importantly, an ending needs to give the reader emotional satisfaction and/or closure.

If all that sounds like a tall order, it is.
I've said it before and I'll say it again: writing is difficult.

Anyone have any tips for writing good endings? In my own work, I've gotten to a place where I don't start writing the story until I know what the ending will be. What do you do?

Good luck with your endings!