Unholy Heights is a cross between Sim Tower and Tower Defense. It takes various elements and places them in this unique and charming monster game. You are the devil in Unholy Heights, and you've decided to purchase a property in the projects/slums.
Your goal is to increase your tenants and fill them up with strong monsters so they can defend you against the hordes of adventurers and heroes that come to try and vanquish the devil.
Creators Site: http://globule.sblo.jp/ (Japanese)
Demo/Buy: http://www.playism-games.com/games/unholyheights/
It's a very nice, fun little game that came out recently.
You can spend hours on this game alone, for four bucks at that!