I use Zaino products -
www.zainobros.com . Not only their cleaners and polish system, but their leather care products as well. I got hooked on 'em when I was into the Corvette scene a few years ago, and haven't looked back. They're a bit more expensive than some other products, but to me the extra cost is money well spent.
If that's not feasible for you, then by all means, go with Zymol. They've been in the leather car business for about 2 gazillion years. Their cleaners work, and the leather treatment is excellent - much better than any of the 'vinyl protective products' on the market.
