Create+a+user+interface

Apps (desktop or web) for interface wireframing and software prototyping

 * [|Pencil], a firefox extension
 * [|HotGloo], wireframing. Commercial web app but with free plan, 1 project with 10 pages, 1 user.
 * Software like Powerpoint or Keynote, where you can easily drag and drop image and textboxes around.
 * [|templatr]
 * [|Gliffy] diagramming web app. Try for free with no signup required.
 * HTML editor.
 * Multimedia creation app like Gimp (open source) or Flash, Fireworks, Photoshop, Catalyst (all paying)

Graphic Design

 * [|Educational Resources for Studying Graphic Design]
 * [|Elements of deign, quick reference sheet]

Grid-based layouts

 * [|Web Culture: Grid-based Layout Designs]

UI Tips

 * [|10 Rock Solid Website Layout Examples]
 * [|12 Useful Techniques For Good User Interface Design]
 * [|10 Useful Techniques To Improve Your User Interface Designs]
 * [|10 Principles Of Effective Web Design]
 * [|Five More Principles Of Effective Web Design]
 * [|10 Useful Web Application Interface Techniques]
 * [|Managing UI Complexity]

UX Tips

 * [|25 User Experience Videos That Are Worth Your Time]

UI Patterns

 * [|Designing web interfaces] companion website for Theresa Neil's book
 * [|30 Essential Controls], by Therasa Neil
 * [|A dozen of Standard Screen Patterns] by Theresa Neil
 * [|Yahoo Design Pattern Library]
 * [|Pattern Tap], a gallery of ui patterns
 * [|Interface Design Patterns], a patter browser

Libs

 * [|10 Beautiful Web UI libraries]

Wireframing

 * [|A Collection of Printable Sketch Templates and Sketch Books for Wireframing]
 * [|50 Free UI and Web Design Wireframing Kits, Resources and Source Files] by SmashingMagazine
 * [|35 Excellent Wireframing Resources]
 * [|30+ Free Web, Mobile UI Element Kits and Stencils for Designers]

Source: http://designmodo.com/30-free-web-mobile-ui-element-kits-and-stencils-for-designers/#ixzz1GHXHOoxZ

Examples

 * [|SkinBase] a community portal to share UI skins