Naidy make a great point - studying sales pages for ideas. Personally I'd also look at the reviews and feedback on products you're interested in - especially any constructive criticism. Because if a product is basically good but 'missing' a key element, you could re-purpose it with a focus on including that missing piece.

Fast product creation itself is easy. It's the research that takes time. If you really want to re-purpose an existing product (s) with your own twist, you need to put the product's methods to use and see how they work. Then you can build in the improvements. Once you've done that, you can bang out an eBook and some screen shot videos in a weekend!