Your line number is there in the bottom left corner of the Arduino IDE screen
You may want to have a look at the free NotePad++
program (it has line #s and much much much more) use it for writing your sketches. Also has a nice Conversion panel to aid in programming. Saves in Rich Text format etc.
You can set the Arduino IDE to use an external editor in Preferences.
When you compile the sketch it reloads the file that you are editing in NotePad++ (of course save the sketch prior to compiling).http://notepad-plus-plus.org/
EDIT: This will make NotePad++ more comfortable with Arduino sketches.
Follow the steps in Post #1 http://forum.arduino.cc/index.php?topic=141050.0