My Simple Surface is a web-based online outliner and planner. Once you've signed up (it's free), you can start creating pages, known as surfaces. Click to create an item, then start typing the text for it. Press Tab to create a child item, or just press Enter to create an item at the same level as the current one.
Right-clicking an item allows you to change its colour and other properties.
Unlike traditional mind maps and outliners, My Simple Surface is more flexible. As you can see from the screen shot below, my test suface has 3 top-level entries, scattered around the page. Only one of them has any attached items. You can drag top-level items around the page, and their child items (if any) follow automatically.
The developer claims that there's an Ipod and Ipad version on the way, which will make this service even more useful for those who have such a device.
Check it out at www.mysimplesurface.com.