You can get a health certificate from your veterinarian or even some PetsMarts and PetCos. Chloe's certificate was around $45.00 from her veterinarian.
At the veterinarian's office they checked Chloe's temperature, listened to her heart, checked her ears and made sure she was up-to-date on her shots. (Make sure to ask for a copy of the shot records, just in case you need to have them for any arising issues.) At the veterinarian's office you can also ask for anxiety pills for your traveling companion if you think your pet would be too skittish during the flight.
The health certificate looks like a health report card, stating what type of animal you have, their weight, coloring, and age. The certificate can also list where you are planning on traveling to with the dates. It will also include the veterinarian's license number and the office's information. :)