Treatment with Leatherique is generally quite good. If you do a search there are plenty of threads on it, including a group buy that just happened earlier this fall. If you apply that once a year (needs to be done in HOT weather and preferably to let it soak in over 2-3 days covered by a plastic bag on each seat) your leather will be awesome.
If you want an off the shelf treatment for several times a year, the Griot's Garage or Meguiar's leather cleaner/conditioning products are also quite good. I get the Griot's stuff at AutoZone or Advance Auto stores; Meguiar's is more widely available.
Cheers,
Gerry