After looking at the stats, we enabled user-driven migrations to Super User and Stack Overflow.
Cryptography is unfortunately right out since it is still in beta and beta sites aren't eligible to be included in default migration paths.
We're also holding back on enabling user-driven migrations to Server Fault since they have a fairly specialized audience and the number of migrations currently going there from IT Security is quite small. We can review this later if that changes.
10/29/2014: since y'all haven't done too badly with the existing migration paths, SF is now enabled as well. Be judicious, and respect everyone involved.