Not free, depending if you 'black' em out or not, but clearing the headlights is still my favorite. I mean, the only additional cost is a 5 dollar can of paint. For the bugeyes, I also like the Kobi, kobi, koby... i don't remember, I'd check, but nasioc.com is down. But he did a custom headlight mod relocating lights using pcv pipe and it looks badass.
I did the foglight mod recently and I like the look of it a lot (running fogs with parking lights).
Coolant throttle body bypass is another one.