Now that we graduated to a full site, we can unlock migration paths to other sites. Remember that moderators can always do arbitrary site-to-site migrations, but regular users can close and vote to migrate questions when they have over 3000 reputation.
The shortlist has a maximum of 5 sites, and one of them is this meta site. How are the other four sites chosen? Do we vote for them?
Original question, no longer valid after Jeff's answer:
This leaves us four other places we can choose (unless my proposal to add tag-based migration paths is accepted). I suggest you add one site per answer, and we see which sites get the most votes (this can be Community Wiki, but reputation doesn't matter on this meta site).