Importing point clouds
First you will need to import your point cloud into Blender as vertices of a single object. There are many ways to do this and many point cloud formats so it is impractical to cover in this tutorial. Personally I convert my data to pcd and then use a pcd importer for Blender.
Creating a bounding cube
The volume material used to render the point cloud has to be applied to a second object that covers the point cloud. I normally just create and scale a cube around the points and then apply the scale/rotation/location.
Creating the material
Make sure you are using Blender Render and not cycles which does not have support for rendering point clouds yet. Create a new material on the cube object.
Adjust the following material setting:
Type to: Volume
Reflection colour: Black
The other highlighted options are also useful for tweaking the look of the output. Check the Blender documents for more information.
Setting the Texture
Type: Point Density
Point Density: Object Vertices
Mapping Coordinates: Global
Influence Density: true
Influence Emission C: false
The radius value is especially useful in adjusting the look of the output.
These default setting work fast and reasonable well on a scene where 1 blender unit = 1 meter with a source point cloud density of ~0.1m. However depending on the scale and density of your input and the desired look you will need to tweak the settings. The main Blender documentation for Point Density Texture and Volume Rendering is worth reading but here are a few point cloud specific tips:
Radius: changes the radius of each point
Density Scale: Darkens or lightens the rendered points
Step Size: lower values result in less noise but longer render times