A mirror, definitely. An under seat bag to carry a spare tube and some plastic tyre levers. A frame pump (why would you not want to carry one all the time?).
Water bottle cage (s). A computer (wireless so you can remove it). Ergonomic grips (if the ones that are on it aren't comfortable).
Bar ends, yes you'll probably enjoy having them. Personally I prefer ones with a decent length of straight after the bend on the top, that way you get more than one riding position from them, and increase their worth.
Have fun with the bike, and happy riding!