Holiday Tipping, What are the Rules?

I've written about tipping before, and around the holidays it's a topic that comes up a lot. Who do you give extra tips to during the holidays? Your mail carrier? Your hair dresser? Your dog groomer? Who else? I think the generally agreed upon rule is that the people you deal with a lot throughout the year who would normally get a tip, should get a little extra around the holidays.

Here's what I want to know, how much do you give? What do you give? Do you give a little extra cash to someone you normally tip in cash (hair stylist, etc)? Do you leave a cash gift for someone you don't normally tip (mail carrier, etc)? Or do you leave a small gift (chocolates, etc)?

Tell us about your holiday tipping etiquette in the comments!