Well, since you asked...
We tip servers. Always, and always starting at 20%. Yes, buffets too. Those servers often work much harder than the "regular" server. Servers share their tips with g-d and sundry, so the 20% isn't fully theirs which bugs me, but I can't change internal systems. We tip on the full cost of the order, not a reduce amount that might be charged as a result of discounts or coupons. Also, if the server is sweet enough to comp something (we have a wonderful server at a local restaurant who always manages to get something taken off our bill!) then we will include that amount in the tip, or at least add it back into the total and tip based on the new total.
Bartenders? Yep. 20% of the total...
Cabbies. Yes. Although I dislike it profoundly, I will tip a cabbie 10% of the fare ON THE METER. If it is not a metered fare, I want an itemized reciept. Yep. I do. And I get them. If they have not added a fee, I'll tip. Otherwise, no tip. I travel frequently and often see "flat rate fees" with added charges.
Housekeepers? No.
Counter service? No.
Retail anything? No.
Personal services like hair, massages, pedicures, manicures, facials, etc? Yes. 10% of the overall fee, unless the person was particularly good then 15 or 20%. For example, one massage included an extra head massage as I'd mentioned a headache that had lingered for days. The masseuse was able to make it go away! She recieved a hefty tip as she took extra time and really provided something of value that would have cost me more otherwise.
I believe that tipping in this country (the US) is completely out of hand, with everyone having their hand out for a tip. I'll tip where it is warranted, but that is it. I don't look for people to tip, and I don't tip based on a guilty conscience! LOL.
Oh, bell hops? $3 per bag... and if there is a concierge who goes above and beyond (like the one in California who found me a rag top on a beautiful sunny day) I'll tip based on the cost of whatever it is that was arranged.
The only bus driver I've ever tipped are those who drive the shuttles between the aiport and the rental car company. They often handle my luggage and put it in the car for me. I'll tip them based on the $3 per bag.
That's all I can think of right now.