[Huzurdaddi]

I find Fiends of Darkness and Devils to be excellent low level summons ( level 2 blood and 3 blood ). The requirements on summoning devils precludes many nations from summoning them though.

For underwater fun Kraken are a fine buy for 3 gems.

While not exactly a low level summon I find that banefire archers are an excellent buy. They are "low" in that enchantment is excellent for death nations.

With Zen's mod the Seasonal Spirits are very nice and worth the gems.