All right, just starting this one out, but I've been thinkin for a while.
This can take place in any time period. I have always imagined Present day, but Im sure it can be easily adapted for the Fantasy era.
It involves otherwordly beings that we call Fiends. They are manifestations of sins and evils. The Seven are their main leaders, the Fiends of Lust, Envy, Greed, Gluttony, Sloth, Vanity, and Wrath: manifestations of the Seven Deadly sins. the Heroes must bring down these fiends, lower fiends (Thievery, Suffering, etc.), and the cult that summoned them (Name I thought of was Order of a Darker Eden)
I've got more, but this is all I can think of right now.