Room Service - I don't tip. They are already imposing 22% service charge + $4 delivery fee.
Bell Staff - usually only use them when I am traveling with family. If they are bringing bags from car up to our room, I will tip them usually $1 per bag or so.
Housekeeping - typically don't tip unless they have done something above and beyond, or I am traveling with family and the family has left the room or bathroom extremely messy.
Valet Parking - usually $2 - $3 out, depending on how long it takes to get the car. If I have called downed 10 minutes prior and I still have to wait 15 minutes when I get down stairs and they are not particularly busy, just slow, the tip will go down to $1.
Regards,
RIP...