Aboard most ships, plan on tipping $8-$9 per person, per day, for maid service, wait staff and other services. This is personally handed to staff the last evening of the cruise (you'll find envelopes placed in your cabin that day). Just consider it part of the cost of the cruise and unless the service was terrible, graciously give it to them.

Tipping is really their pay, and most cruise service staff members make between $65 and $80 per month in salary from the cruise line!