Lexol makes a cleaner and a conditioner that work great- I left some wet gloves in a bag and they ended up moldy and pretty well trashed, but after a Lexol wash and working the conditioner in they look great and are softer than ever. I was amazed at how big a difference it made.

You can find the stuff in most Tack shops (horse equipment)- horse people spend more on leather bridles, reins, saddles, etc than we spend on our bikes.