Flatirons Raceway (Arabians)
Sample Racecard

Uh, you might try to make yours more legible than mine- you can see why I love entering by e-mail (I'm sure the stewards are relieved too!).

About mailing cards:
Always have a spare record at home, just in case the Post Office loses/mangles the envelope or the track goes out of business and vanishes with your racers (hey, these things happen).
Always put your CURRENT mailing address somewhere on the card. Mine here is a bad example since it has my last address on it- if this card were to be found loose by the post office, it would take a while to get back to me, as it would have to be forwarded.
Include as much information as you feel is important while remaining legible. Some people do fantastic jobs using their printers on these cards, which I really recommend.