what's up guys...obviously most of us know about the usual mods that every car should have (y-pipe, CAI) but there are a lot of mods i hear my friends talking about which i have no idea about...mods that aren't cost efficient (cost a lot and don't do too much to your car) but nonetheless mods that sooner or later we'll probably do since we did everything else...

i just want to know what type of mods these are and what you guys feel about them? Examples: pulleys, headers, etc...