People make fun of the owlbear from D&D… But is it really unrealistic? Check this out, scientists (the “mad” kind) have genetically altered goats with spider genes to make spider silk in their milk and haunt my nightmares. Here’s the Cracked article that reduced me to tears, laughter, and screamed obscenities, but it’s not really a joke – here’s the BBC science article on it.
Most of the “template” and “half-whatever” stuff in 3e was kinda lame. But given magic, and a wizard that wants to use it to crossbreed things – the sky’s the limit, as this shows!
Geek Related 
“You’re scared of mice and spiders, but oh-so-much greater is your fear that one day the two species will cross-breed to form an all-powerful race of mice-spiders who will immobilize human beings in giant webs in order to steal cheese.”
From Spaced. 🙂
Mutant Future has taken the idea of Spider Goats and really ran with it.
Dr. Rotwang has a picture.