As always, tipping is at your discretion for the services you receive. When we go to WDW...
at the airport, we don't use the porters there because we carry the bags ourselves.
if using a town car service, we always tip the driver because in our experiences the driver has helped carry our bags from the carousel to the car, not complained if we took a bit longer in the grocery store and provided excellent service. We tip 20% of the total cost of the service, splitting it between the 2 drivers (arrival and departure).
if using Magical Express it depends...IF we tag the bags and let the baggage handlers grab them and send them to the resort, no, we don't tip because we don't know who was the actual person providing the service. IF we don't tag our bags (with the ME tags) and we schelp them to the bus and the driver assists by putting them into and taking them out of the baggage area of the bus, yes, we do tip but only $5.
bell services at the resort...we tip $2 per bag and we usually have 6 - 8 bags for the CM to bring the bags to our room or to take them from the room. I've tipped a CM more on the occassion when they also transported me to a second WDW resort as this is not typically part of their job, but was able to do so when it was slow.
Mousekeeping...we are
DVC members so we don't get daily maid service, but do leave a tip on the days that we do. I'm thinking we left $5 for the trash and towel day (they don't change the bed linens) and more on the day that a full cleaning takes place. When we weren't DVC I think we left 2 or 3 dollars per person in the room.
Table Service restaurants...DH believes in tipping 20% unless the service warrants less. The 2007 and previous years
Disney Dining Plan tipped the server 18% and sometimes DH would leave a little more depending on the situation.
Taxis...it really depends on the driver for us. If the driver is attentive, not letting us sit at too many red lights where the meter keeps ticking, we tend to tip a bit more, but usually we don't tip more than a few dollars since our maximum cost for a taxi has been no more than $15.
Spa services...we tip between 15 & 20% depending on the service received.
I can't think of anything else that we've used that we have tipped. But again, each person is different as is the service a person receives so the tip should reflect the quality of service given.
I hope this gives you an idea! Have a great trip!