With Payment system are you referring to the clients who can make payments on to your website or are you a customer who wants to deposit in a gaming website ? if you are website owner and looking for a payment processor then Neteller, moneybookers, clickandbuy and Entropay are the ones you should integrate with your website
Liberty Reserve !! most of big gambling and casino sites use it. it's easy and safe, since it cannot be cheated.
Are you looking to open up your own online casino or to make a payment to one you want to play at? PM me might be able to help. A lot of the payment processing depends on your staff and other variables.
Apart from the obvious Visa and Mastercard, the answer to this question truly depends entirely on where you customer base is located. Each country really has its own preferred payment methods and mechanisms. For example in Europe many people prefer to pay via bank payments instead of credit card due to low credit card penetration in those markets.
I know a few sites that use only libert reserve , because liberty reserve has its own advantage , i would suggest you use liberty reserve in case of casinos..