[Meglobob]

I like, 'free stuff', which is basically anything that can summon (useful) allies.

A few have already been mentioned but:-

Wraithlord can summon 1 ghost/month. Its not too hard to get 5-10 wraithlords summoning 5-10 ghosts/turn.

Mound Fiends can reanimate free undead.

Call of the Wild Werewolf can summon 3 wolves/turn.

Faery Queen can summon 3 sprites/turn.

The 2 fire kings can summon magma men/fire elementals.

Water Queens can summon water elemental/ernyies.

Draconian Chief can summon 1 Draconian.

Also it easy to spam vine ogres, corpse men and remember to cast carrion reanimation after big battles.