I've seen spectres used with quite a good result. They can become decent stealthy raiders, some of them are also stealthy astral mages to feeblemind these clever mind-hunters, and they can help you diversify into earth-water-astral.
Astral monkey summons are just great. Too bad they come with monkey troops and PD.
Demiliches are quite useful.
Sea Kings are decent mid-game SCs. Their retinue has HUGE upkeep though... May be useful too, for breaking castle walls. Also, they are poison-immune, regenerating and fat, so if you summon two or three sea troll kings, you can use sea troll army with earthquake (rain of stones) and/or foul vapors caster.
Siege golems - for sieging.