Bubbl.us
Create mind-maps either on your own or collaborating with others (free)

Freemind
A desktop application for creating mind-maps written in Java. Must be downloaded and installed (free)

Gliffy
Online diagram software. Create professional-looking flowcharts, diagrams, floor plans and technical drawings (free)

Mindomo
Mind mapping software tool (basic is free, $3 a month for educational pro account)

Mindmeister -
Another web application that allows you to create mind-maps (free basic account)

Slatebox
A Tool for collaboratively creating mind maps and organizational charts (free for teachers)

Spicynodes -
Allows you to create mindmaps or organizational charts with bits of information — such as text, links, photos, and other media — placed into “nodes,” which are then linked together. You can then embed them into websites, blogs and wikis (free)

Spider Scribe-
An online mind map creation service where you can add Word documents, images, maps and more

Xmind -
A mind mapping desktop application (free)

Wallwisher
Wallwisher is an online notice board maker. Discussing a new idea? Taking notes? Giving feedback? Voicing opinion? Wishing a happy birthday?

Stixy
Stixy helps users organize their world on flexible, shareable Web-based bulletin boards called Stixyboards. Unlike most personal productivity or project management software, Stixy doesn’t dictate how users should organize their information. Users can create tasks, appointments, files, photos, notes, and bookmarks on their Stixyboards, organized in whatever way makes sense to them. Then they can share Stixyboards with friends, family, and colleagues.

Lovely Charts
Lovely Charts is an online diagramming application that allows you to create professional looking diagrams, such as flowcharts, sitemaps,etc.