I stayed on civil/friendly terms with most of my ex's.
The last one proved to be a challenge...
At the begining I really didn't want to keep in contact or have anything to do with her. It was a bad break, and she was something I'd just had wanted to forget about...
but after a year or so I tried (At least to my friends and myself...) to keep lines of communication open and possibility of a friendship, but alas I guess it wasn't meant to be