www.sportscarcare.com is a great place to see what Menzerna products and a Porter Cable buffer can do for spyder and swirl marks. The Meguire's three step system one can buy in retail stores does come as a recommendation from others on this list, but I'm thinking the Menzerna stuff is going to be better.
I too have a black boxster and I've bought a PC buffer, the buffing pads sportscarcare.com sells and the Menzerna products, which come highly recommended and are evidently used quite a bit in detail shops.
I'll post before and after pics of my cars after giving them the full treatment of claybar, then the Menzerna final polish II, then Klasse all in one and finally, a nice carnauba wax to keep it all shiny and provide more depth.