Sorry, me again! I'm thinking now that actually it would be good to use a filtered list so users can pick out the resources most relevant to them but am I right in thinking that filtered list only works with pages, not with "Other" items?
I'm looking at this page using the item list includelet which is made up of a combination of pages and others.
Yes, if you want filtering by keyword, such as in the Site Showcase and the Superhighways blog, you need to use content pages for each item, rather than using the Fixed Items that the Item List includelet provides.
In the Showcase I used "Redirect" pages for each item, so that they can be filtered and still send the visitor to an external page.
You can associate an image with the redirect page using the Related Items tab in the CMS.