This comes from the "Unofficial Guide to New York City" 3d. (2002): "Once at the hotel, expect to slip the bellman a dollar per suitcase... When you check out, leave behind at least $1 a day for the maids, $2 a day if the room has a second visit for turndown service or extra care. Tipping the concierge is a question of letting the reward fir the service. If she merely makes dinner reservations, a warm thank you may suffice; if she finagles them in the hottest restaurant in town, or gets opening-night tickets to a Broadway blockbuster, go for the 20% rule." I use $1 as the base rate and work up from there for special conditions and service. $1 a bag for airport porter/shuttle/bellman, $1 a day for maid, $1 for doorman getting cab.