Indigo Studio is a free prototype tool which lets you quickly create functional, animated UI prototypes while maintaining the focus on user experience at every step.
Whether you’re a designer without developer skills, a developer without design resources, or anyone with a great idea – you can design storyboards in real-world context, quickly prototype application design interactions that integrate with your storyboards, annotate those designs, and share your best designs with team members and key stakeholders.
BLOKK is a free font for mockups and wireframes. It helps you create good looking mock-ups and wireframes, where layout is more important than latin words.
Mobjectify simplifies the task of getting up a quick mockup of your mobile website or webapp.
Use the bundled widgets, to generate a prototype for your site in just a few minutes. Which means you can experiment with actually running designs rather than paper layouts or wireframes.
A Wireframe is an important visualization technique for presenting proposed functions, structure and content of a web page.
A wireframe separates the graphic elements of a web page from the functional elements, to visualize and explain how users will interact with the web page.
Wirify is a bookmarklet that lets you convert any web page into a wireframe in one click. It converts all of the elements on a web page to gray boxes, so you can visualize the page as a schematic without content.
Free Yahoo Design Stencil Kit
Yahoo Design Stencil Kit version 1.0 is available for OmniGraffle, Visio (XML), Adobe Illustrator (PDF and SVG), and Adobe Photoshop (PNG).
iPhone PSD Vector Kit
iPhone Starter Kit, a set that comes with several button elements as well as six different iPhone interface options. This pack may be useful for mobile developers and front-end designers who need a professional way to show mock-ups to clients or to work out ideas.