Web
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Mobile
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Research
2012 Review of products on the cloud - http://uxdesign.smashingmagazine.com/2012/05/10/interaction-design-in-the-cloud/
2009 Review but it's pretty good - http://www.sitepoint.com/tools-prototyping-wireframing/
Prospects
Axure RP - $539 and looks to be very slick.
HotGloo - $14/month online based
justinmind - Free version