iPhone blueprint/sketching/drawing software

Does anyone in the SO community know of any software that will let you drag different iOS components around on an iPhone (or even iPad) to help make models or blue prints of app designs? It is only for visual purposes. It doesn't deal with code or anything like that. It's just for positioning and plan开发者_运维问答ning the way an app will look. Has anyone seen or used any software like this?

Blueprint is an app designed for that purpose. I've never used it personally, but I know some folks who think it's pretty sweet.