We are busy squashing bugs right now and doing a lot of polishing and fine-tuning on Fluid UI, our upcoming HTML5 mobile prototyping tool. See our gallery over on flickr. You will find some basic Android and iPhone app mockups and wireframes and it will give you a flavour of creating HTML5 prototypes in Fluid UI.
Please enjoy and be sure to let us know what you think. Signup here for early access.