Lexol, but I'd rather let my bags weather with age and achieve a worn look. That being said I have also used Vinylex on black leather with great results. It's made by lexol too.

 

hd stuff for 3yrs and other conditioners and cleaners when dirty. still look new and leather in good shape.

 

on the Heritage Classic I had, I used a leather / vynil cleaner from an auto parts store and then treat it with protect-all. this stuff works great on leather bags, seats and they say you can use it on the windshield and painted surfaces but I only used it on the seat and bags.
http://www.protectall.com/

I buy it at Walmart in the camper/ Rv product area

 

+1 fpr Maguire's Gold Class Rich Leather, Cleaner and Conditioner. Last bike had a set of cheap bags on it and Maguire made them look great for three years until I sold the bike.