See also this recent question.
(I wouldn't be at all surprised if this is a duplicate, but I didn't find a match.)
Currently, if I vote to close an off-topic question on StackOverflow, I have the option of recommending migration to any of 5 other sites, currently:
I often want to migrate to a site not on the list, such as programmers, unix, or askubuntu.
I know I can flag a question for moderator attention (and that's what I usually do), but why not permit migration to any site?
I'm not suggesting expanding the current 5-item list to 87 (at last count). Just keep the current 5-item list of the most common migration targets, and add an option to bring up a list of all sites. (I'm sure there are more convenient methods than just a list; I'll leave that to you guys to design it.)