There's no one right answer, it all depends on what you can set up and sustain. If you're good with graphics, then maybe making and selling web templates is the best bet. If you're a good writer, maybe writing articles for AC or other sites is the best answer. If you have a good target market that you can offer a service to that doesn't require your constant attention, like hosting, then maybe that is the best answer.
There are many good ways of making a passive income here, just look through some of the threads in each forum and find some that you like, and try them.. keep trying different ones until you find one that you like and is easy, then try a twist on it, or try similar ideas. You will find a method that works for you, but it may not be the same method that works for everybody else.
For example.. don't just jump on autoblogging or article submissions because it's the hot new thing, do it if it's a good match for you. Conversely, don't try to sell web templates if you don't know a thing about web design.. find something that works for you. If you don't understand how something works, then chances are you'll stop making money the first time the system/market changes, as you won't know how to adapt.
p.s. if you're considering writing sales copy for other people as your passive income idea, you may want to keep looking.. your post looks like it was written by a DP script!
j/k! good luck finding your method!
