Flash games.

So sometimes I play games on the internet, and mostly I like them when they are tower defense or some permutation. I wish I knew how to pitch games to flash game design folks, but I don't, so here're two pitches for just anyone of variations on tower defense games:

Frogger, but you are the traffic.
You have some kind of garages or tunnels or any other thing that spawns vehicles. Maybe there's a multiplayer mode where you set up your level and a bunch of folks play as frogs. Player-frogs probably would be extra tough.

Middle School Miscreant. This one is a TD/RPG hybrid.
You design/control a middle-school aged thug in charge of a gang. You roam a neighborhood and as you level up you can recruit followers whom you can position/control. Folks try to leave their houses (homeowners, dogwalkers, young lovers, little kids with nerf guns) or to cross from one end of the street to another, and you have to scare them back to wherever they came from. Every time a person leaves your street (unless they're retreating), you lose rep. If your rep gets too high, cops start to show up. You have to hide from the cops' vision while still terrorizing the neighborhood. If your rep gets too low, other gangs start to invade your territory, and you have to fight them off. The other kids you can recruit will be good at scaring/fighting/hiding to various amounts. There can be a kid who can douse streetlights at night. There can be a kid who has a car that he can pop out of. Also you can buy things like cherry bombs and that your character can use. You can earn money by stealing cable boxes and lunch money.