It's funny that so many say MUD, and here in Belize the mud actually cleans the tires... hhmmm... never would have thought that! Well, I do have to wash them, but they come out looking nice and black, just not shiny.
But when I do want a nice shine, I use Meguire's (it's a cream paste with a sponge applicator, which I don't have here so I'm not sure of the name), it lasts a really long time, even through rain, and doesn't drip like some other sprays.
I've used it for years and it always performs! Makes the humblest hoopty glow!!