OK, basically you tip the valet who gets your car, and the one who brings you your car, as they may not be the same, and they don't pool their tips. We usually tip $2.
Tip the bellhop $1 per bag when he takes them to your room and when he delivers them from your room when your vacation is done.
Mousekeeping: Disney doesn't consider this a tipped position, however, we always tip because we feel that the mousekeepers do a great job and have to clean up messes (not necessarily in our room) that are beyond our comprehension. We usually tip $1/day per person in the room, and more if little extras like washcloth animals are made, or our DD's stuffed animals are arranged creatively.
Restaurant service: 15-20% at all sitdown restaurants, including buffets.
Concierge: have never stayed there, so don't know the protocol.
These are just guidelines, and examples of what we tip, others may have other ideas or guidelines that they follow.
Hope this helps!