You made a thread expecting people to just start listing off their mods for lack of initiative on your part, what do you expect responses to be like? Do you really expect a great number of people to explain how their mods are working for them? Honestly... Browse the forum, look at people's cars and observe how they mod them. You search for the information you want, don't expect people to form and make a massive list for you. It's not a very hard concept to grasp.
People have already told you, angel eyes are probably the number one mod. Any lighting enhancement for the most part and you know why? They are cheap and universal. Not everyone can get zhp shift knobs and short shift kits but everyone here can get $25 smoked corners.