"Farecla G3" and a professional buffing wheel (important). They both should be available in Autobody supply shops. Use a small spray bottle to add a light mist of moisture if and as needed. You can also use the Farecla G10 finishing compound after the G3 but I find you don't really need it unless you're looking for spactacular shine.
For best results, you need to have a proper polishing tool, variable speed and low RPM. Looks like this:
I got one for $70 at Princess Auto a while ago but I don't know if they stock them.
I'm sure you could use other tools but this works very well.