Albion cloak of Magic (one of the earlier dragon quest items)
cloudsong
Bounty Point Cloaks
Darkflame Cloak
Magma Imbued Cloak (golestandt drop)
Leviathan Cloak
Kraken cloak
Those would be at the top of the list in terms of utility. It really depends on the rest of your suit and if you are interested in +11 skills in template if you decide to use some of them, because many of those cloaks have +3 or +4 skills in them which is nice for most casters, but theurgs often don't care about that if not air specced.