There are obvious ones (eg FDO) and not so obvious ones. So throw out your suggestions and I'll edit this as we go. Then we can ask Scott which one he likes best once the thread gets stale.
FDO = Future Dark Overlord or Francis Donovan Olivieri
PS XXX = Pope Siglericus XXXth
GEFS = General El Fontaine Siglerisimo
LPT = Lord of the Plaid Tanks
CDO = Crack Dealing Overlord
FIDO = Future Intergalactic Dark Overlord
GOD = Generally Omnipotent Divinity or Guy Of Doom
SFS = Scott Fuckin' Sigler
PDE = Pimp Daddy of Evil
TERROR = Terrifically Extravagant and Really Really Outrageous Ruler
Okay, that's what I can come up with off the top of my head. I'm sure I missed a few.
Prøducer øf Døøm, Høst øf Tuesday Terrør, Funky Name Brutha, Retired Gutter Brethren & Tangential Tyke