Deleting every material from a file.

I have taken up an old project again.
I made a mess of it last time. The objects have useless names, there are tonnes lot of useless lamps, cameras, materials, etc, so its quite a pain to work.

I have deleted the lamps and other stuff and given useful names manually, but there are still loads of useless materials.
Is there a quick way to delete them without removing them from every object they are assigned to?
Or a way to import just the objects without their materials? I want to continue with just the models in that file.

One quick way to reduce material count is to select all the objects and link the materials using CTRL-L Then all objects will have a single material. Save, Close and re-open your scene and you will now have only one material to deal with.