I read that one of the best (and cheapest) solutions is to apply any product which contains DEET, such as Off. You are supposed to apply a light coat and let it dry. Several coats are needed, but people swear by how good of a job it does.

Here is one copy and paste from one of the forums I've read this on.

This is gonna sound crazy, but here goes. I did the routine of ridding my headlights of the oxidation but it didn't take long for the haze to come back. Well, the other night I was spraying some bug spray (OFF Sportsman brand) on myself before I went outside and didn't notice that I accidently sprayed a little bit on my car headlights which was behind me. About 2 hours later I come back inside the garage and noticed that where the overspray is on my headlight it is totally clear. A light bulb went off in my head and I sprayed some on a rag and wiped the headlight down being very careful not to get it onto any painted surface and I was amazed to see how well it worked. That was 2 weeks ago and NONE of the haze has come back so far, though usually it would have already begun to haze up again. Just thought I'd share this. I'm gonna keep an eye on this to see how it loox later on and I will keep you posted.