My (least?) favorite is CGK, which has has no obvious correlation to any of "Jakarta", "Soekarno-Hatta International airport", or "Indonesia". It took a bit of digging to figure out that it stands for Cengkarang, the name of the hamlet it was built in...
FWIW, "JAK" is Jacmel, Haiti, but "JKT" is Jakarta Metropolican Area -- kind of like "NYC", except that there's only one international airport in Jakarta, making it rather useless!
[This message has been edited by jpatokal (edited Jan 06, 2004).]