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

This kan be done in many easier ways. Here is a oneliner:

do shell script "date '+%Y-%m-%d %H:%M:%S'

@Jorsta Wow! My solution is, however, pure AppleScript.

Right! This is basically doing the same thing as your script, but shorter.

on run
	set now to (current date)
	set dateString to "" & year of now & "-" & my twoDigit(month of now as integer) & "-" & my twoDigit(day of now) & space & my twoDigit(hours of now) & ":" & my twoDigit(minutes of now) & ":" & my twoDigit(seconds of now)
	return dateString
end run

on twoDigit(theValue)
	if (count theValue as string) is 1 then set theValue to "0" & theValue
	return theValue
end twoDigit