there are so many products out there to clean tack, but the key is to know what your tack actually requires, and when it requires it.  The key ingredients i swear by are beeswax, lanolin and oils such as coconut and even train oil.  These are important for maintaining flexibility, resistance to wear and tear and increasing the life span of your leather's career.

The initial products i would recommend are Effax and Veredus for everyday use, and K0-cho line for leather that is going into storage (i.e. a horse coming out of work due to injury, going into foal etc) or for times when it could be exposed to damp conditions.

Stubben Hammenol is good for leather that is strained a lot in riding, especially stirrup leathers, who can be damaged by constant running through the stirrup bar.  The hammenol can be used sparingly all over the leather, and can soften the leather and prevent/get rid of the 'bits' of leather spurs/fragments that can be left from the daily stresses.