Did you overdo your dog's nail trim? Bleeding toenails can often times be remedied with some household ingredients. A small amount of flour packed onto the end of the nail will often quell the bleeding. Also try rubbing a bar of soap on the end of the nail for the same effect. Nothing, however, beats having a stash of styptic powder, which you can buy at your local pet store or at your vet's office.
For more information, please read the story How to Trim Your Dog's Toenails.