Apple's Human Interface Guidelines continue to be a good resource:
Buttons & Labels: http://developer.apple.com/library/mac/#documentation/userex...
Alert Dialogs: http://developer.apple.com/library/mac/#documentation/userex...
edit: It's also cool to see how much has (and hasn't) changed over the years. Here's a 1995 version of the Macintosh HIG: http://dropbox.scripting.com/dave/misc/appleHumanInterfaceGu...