I almost always tip just over 15% to what ever evens out the bill. Unless it is the typical Chili's type lunch that comes out to $14, I always leave $3. I think 15% is fine and most people think that signifies a good tip. I don't feel cheap leaving 15%.
My hair cuts cost $15 and I tip $10
Usually give the valet a couple of bucks when I pick up my car, same goes for hotel porters
Bartenders get $1 for 1 beer, cute girls get more.