The golden rule seems to be that cash is king. That being said, a small gift demonstrating that you know people's likes and dislikes is a nice touch, usually best appreciated when given in addition to cash inside a card. Don't give liquor or chocolates unless you know it is a favorite item of the recipient. If you don't like to give cash there are now gift cards for everything under the sun including, Starbucks, Dunkin' Donuts, gas stations, local restaurants, town parking meters and more.
There are people like your nanny, housekeeper, driver or dog walker that you may depend on everyday. In this instance a holiday tip more closely resembles a corporate bonus. Depending on their length of service, cash or a gift equal to one or two weeks of salary is the minimum and can be significantly more if they are a long term employee.