And the only sensible answer you would ever receive should be "anything that people want to pay repeatedly for" :)

My point being. I don't think anyone would give you a specific idea for recurring income cause then they would go ahead and do it themselves.

I might be wrong but I doubt it.

Good ideas to make money are a dime a dozen -- just look at android forums.. there are a million ideas that could make money..

Seeing real examples can sometimes give a better idea of what an idea is really worth, with real numbers, not what a concept could be worth IF(and a BIG IF) people really want to buy it, or visit it, or download it..etc... 1 Real life case study is worth 100 ideas for apps/businesses.

Sort all the answers to this topic by revenue and your question will be answered.

Any idea which hasn't been proven to work already is practically worthless. You're better off looking at cases of existing successful passive income and emulating those.

Then, you can tweak it, one small change at a time.