A list of most useful Wireframing/Mockup tools on the web.

1.- Axure: Axure enables application designers to create wireframes, flow diagrams, prototypes, and specifications for applications and web sites.
axure

2.- MockFlow: allows you to design and collaborate (in real-time) user interface mockups for your software and websites. It comes with numerous built-in components & icons.
wireframepro

 

3.- Pencil Project: The Pencil Project is a free addon for Firefox. Some key features include: built-in stencils, multi-page document support, and multiple export options.
pencilproject4.- Balsamiq Mockups:Using Balsamiq Mockups feels like you are drawing, but it’s digital, so you can tweak and rearrange controls easily, and the end result is much cleaner.
balsamiqmockups

5.- HotGloo:HotGloo is completely web based with lots of features that let’s you drag and drop and scale items easily. It also has support for realtime collaboration.
hotgloo

 

6.-  Cacoo: Cacoo is an online drawing tool that allows you to create a variety of diagrams such as site maps, wire frames, UML and network charts.
cacoo

 

7.- Mockingbird: Is another web app with a focus on collaboration. It allows you to link multiple mockups together and preview them interactively to get a feel for the flow of your application.
mockingbird

8.- Protoshare:  Is an easy-to-use, Web-based prototyping tool with a focus on collaboration. Team members can review work and provide timely feedback, ideas, and suggestions on clickable wireframes or creative content.
protoshare

 

9.- iPlotz: Allows you to rapidly create clickable, navigable mockups and wireframes for prototyping websites and software applications.
iplotz