Jumping in late and attempting to answer the original question without debating whether any of this is "appropriate" or not:

The standard tip in any restaurant with waiters is 15%, perhaps then rounded up to the next whole dollar if you're happy. (Note: if you're computing your tip after the tax, you're already giving them a bonus.) Some restaurants add an "automatic" gratuity to your bill, particularly for larger parties, so do pay attention to the bill. If you deliberately tip less, that's a signal that you were unhappy with the service.

Tipping taxi drivers is a bit more complicated. I've heard 10% as a metric or "round up to the next dollar or two." The specific taxi tipping custom also seems to vary from city to city. Similarly, for getting a haircut, there's an expectation of a tip for fancy (women's) beauty salons, but not for basic (men's) barber shops. Since I frequent the latter, I can't say much about the former.

If you use a valet to park your car, even for "complementary" valet services, you typically tip the valet a dollar. If it's a swank restaurant, maybe $2 or $3. Bellhops (the guys who helpfully offer to carry your bags into the hotel) typically also expect a tip. I believe the answer is $1/bag.

If you're at some kind of uber-trendy restaurant or nightclub, of the sort I don't really frequent, tipping customs get quite particular. It's not unheard of to push a $20 or more to the maitre d' to get you in sooer, but some places will see it as an insult. Tread carefully. Similarly, it's not unheard of to tip a valet extra bucks in advance to have your car parked right up front. Needless to say, these sorts of customs are restaurant-specific.

If you go to an espresso bar (Starbucks, etc.) or many other restaurants where you order at a counter, there will typically be a "tip jar" on the counter. I typically dump in whatever change they hand to me after buying my coffee. This is entirely optional.

I've even heard of leaving money on your hotel bed to tip the ladies who clean up your room. I don't typically do this, but a friend of mine who does leaves $1 for each day.