Are there any UI/UX Prototyping tools which are used by any of you seasoned Maemo developers? I'll use everything from MS Paint, to PowerPoint/Visio, to even coding something with HTML/CSS3 if it would make the point. But, am just looking for something that would be easy enough for a developer to take and pretty much craft the functionality in a straightforward manner.

I do realize that Maemo is not the primary development environment for many of you, and so other platform specific tools might be recommended here - and that's ok.

It would be nice if there is a tool (or two, three...) that are used which can be further refined for Maemo 5 and beyond use. And it would make it a heck of a lot easier when doing those initial brainstorming topics to be able to have an application that one can use to better detail aspects of an idea that is more on the GUI or user-process level.