*Wait staff- 15% is the norm. I usually like to tip 20% because I was a waitress back in the day and I know how absolutely difficult it can be. I personally feel that 10% is the lowest to tip and this is only if the service is really crappy. I know some people who don't leave a tip at all if the service is really crappy. I have to disagree with this because you don't know what else that person has going on that lead to the service being crappy. The only time I feel like it's absolutely ok to not leave a tip is if the server is outright rude to you. In that case I would ask to speak with a supervisor.
*Bartender- I usually tip a $1 a drink if I'm not opening a tab and 15%-20% if I'm paying an entire bill. If you're at a PACKED bar, try tipping a bit higher and you may find that you get better service.
*Valet- $2-$3 is usually recommended for a valet.
*Mani/Pedi- %15 is usually recommended for a mani and pedi. The nail place by me charges $20 for both a mani and a pedi. However, usually there is one person doing my mani and one person doing my pedi. I usually give $3 to each person.
*Eyebrows- At least $2. Eyebrows are usually pretty inexpensive to get done so 15% would be a very small amount. I recommend at least $2 and probably more if it's a place you go to a lot. You don't want to leave with janky brows!
*Spa services- Again the standard 15%-20% is recommended.
*Hairdresser- 15%-20%. This rule still applies if you have someone doing a separate cut and color. For the person cutting your hair you give a percentage of the haircut price and the same with the person coloring your hair.
*Shampoo girl- $2 is recommended, but I usually give more. The shampooers do a lot of the grunt work and yet the scalp massage is my favorite part of getting a haircut!
*Housekeeper- When you're staying at a hotel it's recommended to tip anywhere from $2-$5 a night. If your service is amazing, tip a bit more.
When using a service where a Groupon, Living Social Deal, etc. has been purchased you MUST tip on the original price of the service. The person doing your massage shouldn't get tipped less because you scored an amazing deal on Groupon.
Try not to tip on a credit card. I know I hate carrying around cash and am guilty of leaving tips on credit cards, but tipping in cash makes it easier for the person to take home the money immediately.
Source: Emily Post
Do your tipping guidelines differ from the ones above? Have you ever NOT left a tip?