Lexol works really well and is easy to find but the best stuff I have found is Aussie Leather Conditioner. Just a note though, if you are using it on the seat pictured in your signature you are wasting money because that seat cover is vinyl
Part of my '05 OEM seat has leather strip between rider/passenger portion...
To answer the question, I use Pledge on my seat. Guess my *** is too fat, creating enormous contact patch between *** and seat that doesn't allow slippage. Or, could it just be the amount of body weight forcing down on the seat? Either way, I don't slide around on my ***!