A AppleScript to generate a password.

passgen.scpt

repeat
	set passwrd to {}
	display dialog "How many characters do you want this password to have? NOTE: Don't enter anything other than a number." default answer "64" buttons {"This amount"}
	set char_amnt to text returned of result
	repeat (char_amnt) times
		set end of passwrd to some item of "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
	end repeat
	display dialog "Your password is:" default answer passwrd as string buttons {"Copy to clipboard and quit", "Another one"}
	set the_button to button returned of result
	if the_button is "Copy to clipboard and quit" then
		tell application "Finder" to set the clipboard to passwrd as text
		error number -128
	end if
end repeat