Instructions are at the bottom if you are lazy and don't want to read alot.

Well, I think I finally figgured out a good way to get that yellow fog out of old headlights. Sorry, I don't have any before/after pictures (digital camera is really bad), but believe me if you take your time it will look much better. I did research on the topic and I found acouple recommendations, but for some reason none worked for me- well, atleast to my satisfaction. I tried some 3M Rubbing compound that gets scratches finer than 1500 grit out, fingernail polish remover, acetone, bleach, rubbing alcohol, paint thinner, and the strongest plastic cleaner I have ever seen, but still had some fog. For the most part, the yellow was gone, but I was not happy with the left over fog. So, I looked more closely. It seemed as if there was a thin film of gunk on the headlights, so I figured I could sand them down- and that was the trick.

FOR ALL THOSE WHO DON"T WANT TO READ ALL THAT- here is what you need to do.
You need to go to a local autoparts store and pick up some 3M Rubbing Compound (gets scratches finer than 1500 grit out) and some 320, 400, 600, 1000, and 2000 grit sandpaper, and its just basic sanding from here on out. I've found that it works much better to remove the headlight and bring it to a table or somewhere that you can mess with it easily, rather than keeping it on your car. Start out with the 320 grit and work your way up. Its going to take alot of sanding for the higher grits but if you take your time you will be pleased with the results. I wet sanded at 2000 grit after I dry sanded to get the scratches even finer, then used the rubbing compound to get the leftover haze out. You also might want to have a wet rag with you to wipe off the residue from the plastic after finishing each grit. Good luck!