AppleScript to get current date and time (YYYY-MM-DD HH:MM:SS). Usable as a Text Service in Mac OS X.

current-date-and-time.applescript

(*
	The zero_pad function taken from:
	http://www.nineboxes.net/2009/10/an-applescript-function-to-zero-pad-integers/
*)
on zero_pad(value, string_length)
	set string_zeroes to ""
	set digits_to_pad to string_length - (length of (value as string))
	if digits_to_pad > 0 then
		repeat digits_to_pad times
			set string_zeroes to string_zeroes & "0" as string
		end repeat
	end if
	set padded_value to string_zeroes & value as string
	return padded_value
end zero_pad

on run
	set now to (current date)
	
	set result to (year of now as integer) as string
	set result to result & "-"
	set result to result & zero_pad(month of now as integer, 2)
	set result to result & "-"
	set result to result & zero_pad(day of now as integer, 2)
	set result to result & " "
	set result to result & zero_pad(hours of now as integer, 2)
	set result to result & ":"
	set result to result & zero_pad(minutes of now as integer, 2)
	set result to result & ":"
	set result to result & zero_pad(seconds of now as integer, 2)
	
	return result
end run