Here are some on Xerxes...because I've only started studying him so far...
1) (About how Xerxes could never be satisfied)
" ...All his cavalry and infantry and fleets of ships...were not enough to satisfy him. And so he offered a reward to anyone who could discover some pleasure that was altogether new. Yet, even if such a thing had been found, he still would not have been content." --- Cicero 'On the Good Life' 7.19
2) (on his great achievements)
"Xerxes above all the kings of the Medes and the Persians who came after him used the greatest intellectual power, his achievements were glittering."--Pausanias 3.8
3) (about the need for more evidence)
"If we had only the archaeological and epigraphic evidence we might well take the reign of Xerxes as the golden age of the dynasty."---Burn, A.R. 'Persia and the Greeks: The Defence of the West" pp. 313-315
4) (about Xerxes' good and bad points)
" Xerxes was tall and of noble bearing, but he was violent, sensual, weak and indolent."--Huart, C. 'Ancient Persia and Iranian Civilization.' p60
5) (about Xerxes never being as good as his predecessors)
" Xerxes was a powerful figure, but it would seem that he never lived up to his early promise and was certainly never the king, or perhaps the man, that his father Darius had been."--Young, T.C. "The consolidation of the empire and its limits of growth under Darius and Xerxes" p 71
That's all for now, I'll be back with more Xerxes and hopefully other quotes for the Spartans, Minoans and Persian kingdom later on. Hope that helps someone out there!