Isn't there a chapter in the manual stating the compatible flashes? Should be the first reference, 2nd one can be any Canon website where you can see all details about the camera and flashes. ETTL-2 doesn't come with your 500D, it's there already for quite some years (my 350D already has it and it wasn't the first camera) and it's nothing but the communication protocol between camera and flash. It's rather up to you "to make full use" of your equipment.