It's not easy to choose some "good" tool for UI prototyping. There are a lot of freeware and payware solutions.
So, we've got dilemma.
I've choose the next directions:
- free tool for easier prototyping UI stuff
- or tool which can be used in other areas, so, knowledge accumulated with UI prototyping can be re-used.
- 10 Minute Mock Prototyping – Tips for PowerPoint very interesting post, worth reading.
- PowerPoint Prototyping Toolkit (release 0.2)
- Interactive Prototypes with PowerPoint tutorial for creation prototypes with interactions (mouse click, mouse over, etc.)
If you choose to use PowerPoint, you should collect some UI components library for easier UI composing, etc. I've found several good examples.