Zymol makes a product for leather called Treat. I really like it. It contains collagens and stuff that's supposed to be great for the leather.
Oh, and it smells like BANANAS - mmmm!
More information about Treat, taken from Zymol's website at
http://www.zymol.com/treat.htm
Sunlight, heat and everyday use will permanently damage the delicate finish of
your leather upholstery.
The denaturing process of leather tanning
removes precious moisture residing in the hide. Introducing solvent-based conditioners accelerates aging in leather upholstery and trim. zymöl Treat Leather Conditioner is a solvent-free, banana-oil and collagen-based feeding product that releases trapped solvents and restores moisture to keep your leather looking, feeling, and smelling like new.
Contains Beef Collagen, Banana Oil, Lemon Seed Oil, Coconut Oil, Cetyl Esters, Cetyl Cocoamide, Lecithin and Aloe Vera Extract.