My headlights weren't terrible but had a yellow haze for awhile now and I read good reviews on this stuff so I decided to give it a go. Walmart had it for under $7 (+$2 for the pads, but you can use any microfiber towel) and it took all of 5 minutes to do and cleared them up nice. Reviews claim that just 1 use lasted people for years, but even if I have to re-do it ever, it seriously is quick & easy to do:
(left light before, equally as bad as the right)
(right light after)
(all the residue left on the pad)
(left light before, equally as bad as the right)
(right light after)
(all the residue left on the pad)