If you are visiting Disneyland for someones birthday go to City Hall on Main Street first. They will give you a Birthday Button for free! If you wear it through the park cast members will wish you a happy birthday. There is also an old fashion phone on the counter in City Hall. This is Goofy's private line and he will wish you a happy birthday too!
City Hall also passes out other types of buttons:
1st Time Guest
I'm Celebrating (We has one of these)