What vaccinations do you consider important?

[brahma02]

I plan on breeding, showing and selling hatching eggs. I have have hatched chicks a couple of times before, but diseases have never crossed my mind. I haven't had any problems in the 5 years that I've own chickens, but now if I start showing and stuff, I imagine they will be exposed to different agents. I have chicks hatching soon and from what I read, most vaccinations should be given to day old chicks. So, are there any required vaccinations? Are there any that are fairly important? I don't want to spend a lot of money, but I do want my birds to be protected.