The headlight lens on my Acura RSX gets foggy being an old car.  I purchased Meguiar’s Headlight Restoration Kit based on good online reviews.  Think I picked it up at Walmart in the US though it is available at Canadian Tire and Amazon as well.  The kit comes with a buffing pad you attach to your drill, polishing cloth and polishing paste.  It is pretty easy and quick to use and has excellent results.  I do need to repolish every year though.

Update: Further research indicates the headlight get yellow because of UV and that the factory installed clear coat has worn off.  There are multiple youtube videos on how to apply a clear coat to your lens so you don’t have to constantly restore it.  Will be a project for the summer.