The suggested amounts can be viewed here:
RCCL Tipping Guidelines
RCCL still uses the "cash in envelopes on the final night" method as their primary tipping procedure, however at any time during the cruise you can simply have these tips added to your onboard account (and therefore paid by credit card) by calling or going to the guest relations desk. You will get cards to put in the envelopes for the last night presentation of tips, which will show the amount you have given to the person via your account. I like RCCL's system because it allows the guest more control as opposed to those used by other lines which default to the automatic charge for tips to your account.