Any of the ones from Corsair or Enermax.
450W Corsair (min 80% efficient) - £44.16: http://www.ebuyer.com/product/131052
425W Enermax (min 82% efficient) - £51.69: http://www.ebuyer.com/product/144083
450W Corsair (min 80% efficient) - £44.16: http://www.ebuyer.com/product/131052
425W Enermax (min 82% efficient) - £51.69: http://www.ebuyer.com/product/144083