Trd spoiler, slotted rotors, rebadging, fog lights, 4th brake light conversion kit, and high mount 3rd brake light are good cheap mods that really add a lot to the cars look. I personally don't recommend changing headlights and taillights, as non oem plastics tend to yellow and fade pretty bad. Louvers are a taste thing. I like them but I wouldn't put them on my own car for visibility reasons. I've thought about a racing stripe too but haven't done it. I think a thick white double stripe down the middle could look really cool on the black but that's a taste thing as well. If you like it try it, it's reversible and cheap.

Also look into interior mods, pretty much everything on the inside can be replaced with other better parts. I would list as the ones I've done but that would take forever. My favorite thing I've done though is swapping all the amber LEDs to either red or white to match the rest of the car LEDs. That was very cheap, looks great, but you need to learn to solder to do that. I learned to solder for that project though so it's definitely not a hard thing to do. Also black JDM trim for the interior looks nice. They're cheap if you get them from a dealership website but there are a lot of small pieces that add up.

Check out the ft86club forums for more projects, I find new things to do all the time on there.