Well that depends on which G19 we're talking about. On my Gen4 carry gun, Trijicon HD sights and factory minus (-) connector. On my Gen4 competion gun, Warren/Sevigny sights with fiber optic front, and Vogel competion trigger system. My Gen3 has Trijicon sights, Talon Grips, and and a butt plug.
Having said that, I don't recommend changing anything unless there's good reason. Except for the sights of course, Glock sights are terrible.