http://www.dogs-r-us.org/ - about the reality of the nightmarish breeding conditions behind a dog in a pet shop window.
http://www.puppywatch.org.uk/ - more about where pet shop puppies really come from. Upsetting.
http://www.dogstrust.org.uk/az/b/batteryfarmeddogs/default.aspx - the Dogs Trust campaign against battery farmed dogs.
Arguably no animal should be sold in a pet shop: it's difficult for shops to provide appropriate care and the right environment. But selling dogs - big animals with specific needs and lots of teeth - purely on the criteria of ' has this person got money' is insanely stupid.
I foster rescue dogs. So far, I have not volunteered to foster an ex-puppy farm dog. This is because puppy farm dogs are popularly reputed to be bloody difficult and I know my limits. Buying a puppy farm dog - and don't fall for the line that dogs in pet shops are anything else - it is wrong, encourages a horrible industry, and may well leave you with a dog that is scarred emotionally or horribly ill. Yes, they come with guarantees. But who takes a living sick puppy back to the shop for a refund?