I really like the world apotheosis, but for some reason I think it sounds a bit awkward as a guild name. ^^;;
My favourites are Euphoria, Hysteria, Elegance.
Off from a.L's list, I also like the words
Delirium,
Rhythm,
Equilibrium,
Silence,
Reticence. (sounds good, but means shy. LOL)
Seems like words from my list have very similar ending sounds. =_=