TwilightCat - TwilightCat's site hosts some excellent agents with graphics by Trollop or Bug.
The Palace of the Evil Shee - Lis Morris is probably the greatest 3rd party developer for the Creatures series. Includes GAIA for C3 and the Canny Norns for C2. A shame the site seems to be knackered at the moment.
Wafuru's site - Wafuru was the definitive 3rd party sprite artist. She has recently released another C2 breed, the UniNorns!
Non-Creatures
UKIP - Down with the international bureaucracy!
Rathergood - funny site
weebl - another funny site, with badgers on it
Urpney - (classification x) fansite of the armour-wearing villains of the 1990s cartoon, the Dreamstone. Big sweaty blokes in armour, and , ahm, big sweaty blokes out of their armour.