For cleaning, I use saddle soap. It works well, and does some minor conditioning of the leather.
If the leather is starting to dry out, or if I want to water-proof it more, I will use some mink oil or I will use Biwell leather dressing. The nice thing about Biwell is that if you apply it with your bare hand, it will liquify a good bit and penetrate the leather better. For mink oil, I usually melt it down over a stove and apply it in a liquid from. Both products will leave a little residue when you are done, so I let them sit for an hour or so and then wipe off the excess. I have used both of these products on all kinds of leather apparel, even hiking and riding boots. A word of caution, do not mink oil or Biwell on your saddle or on the butt of your pants - it can be a little slippery after you first apply it.
k_enn