1. Bell Hop Takes your Bag to Your Room: $1 per bag (although I normally take my own bags)
2. Housekeeping on a ONE NIGHT (in-and-out) stay: nothing, that's their job (although I normally don't take housekeeping for a one night stay)
3. Housekeeping (per night or at end) on a multi-night stay: nothing, unless I left a particularly messy room, in which case, $5
4. Housekeeping on a multi-night stay when you do Green Choice (say 5 days using GC. What do you tip at end of stay?): no idea what Green Choice is
5. Valet takes your car: nothing, that's their job
6. Valet goes and gets your car: nothing, that's their job
7. Concierge helps you out: nothing, that's their job
8. Front Desk person goes above and beyond (scores a great suite, slips you drink tickets, etc.): both of those sound like bribery to me. I know it is common practice in Vegas, but I would certainly not participate.
9. Wait Staff when they have already included a 20% tip on the bill: nothing, since it's already included.
10. Club Lounge Attendant: if they pour you a drink, then perhaps $1 in the US (like at any other bar). In foreign countries, depends on local custom
11. Server when you are at a buffet (they bring coffee, juice, then bring bill). 10% of bill