Mario Kart DS: 545655700918
Just had a blast playing Kart DS online - my opponents generally wiped the floor with me (the fact that two of them had kana in their IDs is probably a good indication of their geography and skill).
I don't know how FFIII really works online yet, but at first glance it seems to be another implementation of FFIX's Mognet, the twist being that this Mognet is actually connected to the real Internet, so if you have FFIII you can send me messages and vice-versa.
I'll post these codes (and codes for other games as I get them) in the contact page of my website. If you only have sixteen ways to contact me, and still feel that you could use another, here you go.
Edit: I think I'll have to be more conservative with my LJ tags from now on. I've just hit the 1,200 tag maximum. Sigh.