New Scientist has an article headlined Cheap, safe drugs kill most cancers. The drug in question is dichloroacetate (DCA), which is already used for other maladies. Scientists will have to investigate this thoroughly, but the good news is that this material is inexpensive.
The blogger Orac has some reservations. He points out DCA has only been tested in cell culture and rats and that cancer is not a single disease, so it would be unrealistic to expect a miracle cure (or any cure) for all cancers.