My Toyota Soarer has full beige leather interior and the carpets and tailored mats to match which I'm sure would look really nice if they didn't look like they were capable of growing spuds in. I've tried some carpet cleaning foam from under the sink but it's not made much difference.

What do people recommend?

I use this P21S Total Auto Wash on my royal blue matts and they come up loverly.

If they are pretty grubby then I would recommend spending £30-40 on a proper interior valet rather than trying a DIY job. Shampooing the carpets and mats will likely make a world of difference, but the important thing is to ensure as much moisture is removed again afterwards (otherwise mildew can set in), and to do this, a wet and dry vacuum will be needed, which most decent valeting companies will have to hand. :)