Interface Prototyping Tools

Pencil Project
http://pencil.evolus.vn/en-US/Home.aspx

Verify
http://verifyapp.com/

Web Site Wireframe Tool
http://wireframe.talltree.us/default.asp

Mockingbird
https://gomockingbird.com/mockingbird/

fluidA
http://stage.fluidia.org/

fluidUI
https://fluidui.com/

Cacoo
https://cacoo.com/

Lumzy
http://lumzy.com/app/

iPhone Mockup
http://iphonemockup.lkmc.ch/

Google SketchUp
http://www.sketchup.com/product/newin7.html