Sjra Wagemans thinks they are a calendrical device.
Lloyd Kilford on the Bonn dodecahedron.
The Druidical Research Institute has an overview (in Dutch).
Good article in French.
The Kenchester dodecahedron in Hereford.
Another from Gill Mill in Oxfordshire.
Here's one in Limerick (though I suspect originally from France)
A squashed one in Newcastle-upon-Tyne.
George Hart has nice pictures including an icosahedron as well.
A German schoolkid's essay on the one from Schwarzenacker in the Saarland.
Paul Garland's Flickr photos: 1, 2, 3, 4