• (IMP)- Each imp sacrificed reduces the cost of every subsequent imp by 150 gold (I like making about 25, myself)
• (FLY/SPIDER)- Sacrifice both of these for a free Warlock
• (FLY/FLY)- Current research is immediately completed (save them for later in the level when stuff is harder to research)
• (BEETLE/BEETLE)- A two beetle sacrifice completes your current manufacturing project
• (BEETLE/SPIDER)- Free Dark Mistress
• (SPIDER/SPIDER/SPIDER)- All three ot these just for a measly demon? do it if you want to...
• (DARK MISTRESS/BILE DEMON/TROLL)- FREE HORNED REAPER! >> (HORNED REAPER)- All your creatures become angry
• (BILE DEMON/BILE DEMON)- All your creatures are turned into chickens for a limited time! (only do this if you don't want your creatures to go to an armageddon... chickens do not heed it's powerful call)
• (GHOST)- All your chickens are killed
• (VAMPIRE)- All your creatures become diseased. Happy Sacrifice!

Note... These do not have to be back to back... you can spread them out. (Beetle/fly/beetle/fly still gets both projects completed, for example)