I would like to present here one tool I have developed recently for visualizing vectors in three dimensions. The tool allowes not only to view vectors but also to share them with others. Check the "link to current vectors" for that.
You can view it only by visiting URL: www.bodurov.com/VectorVisualizer
The tool is build from scratch and does not use any 3D engine. In fact it includes a very simple light weight 3D engine for drawing lines in 3D. For the platform I chose Silverlight under C# as I find .NET to be the best coding environment.
If you want to dive deeper into the concepts that this tool is based on you can check my Simple Talk article