I've been slowly growing a stack of maidens (14-->31 and counting) using sacrifice and thought I'd post about it in case anyone isn't aware of this trick.
First, about the spell. Sacrifice has a base damage number and a sacrifice number. You do the base damage to a friendly target and use a percentage of that damage to create new units in another stack. If you give the target stack enough HP to generate a full creature you actually give them a permanent +1 to the stack size. Level 1 sacrifice has a 40% conversion rate, so to get back 1 maiden you need a sacrifice spell that does at least 375 damage (150hp/.40).
Roam around and look for easy fights. Engage them, and don't cast until it's your maidens turn. Cast sacrifice on something you know your maidens can resurrect to full. They'll die, your maidens will increase in size, and then, immediately have your maidens use Call of Valhalla to cure the victim back to no-loss. Note you can't sacrifice summons or things you hatch from an egg. In the old days you
could sacrifize something you hpynotized, but I don't have the spell yet to see if that cheesy trick still works.