I don't think any of the 'big spoilery names' like Azem will work just due to the risk of people googling it. So far the theme has mostly been setting monsters and summons, with the major exception of Louisoix.

If we wanted to keep on that theme we are running out of iconic enemies, though we have a few (Sin may not work great as a server name, but Yevon would, for example). I think going for some setting elements (ex: Materia, Esper, ect.) would be neat, as would be adding the names of heroes and organizations (ex: Locke, Cecil, Returner).