Note that most taxis, from the airport, will turn on the meter - take the expressway to get to the hotel as it will be faster & overall cheaper. Note that if you do this, there is a toll (not sure what it is off the top of my head) that you will have to pay - so make sure you pull some baht notes out at the ATM at the airport - smaller bills are better. Any taxi that you get from the hotel will also use its meter - the ones that you pick up of the street won't use their meters & you will have to negotiate the prices.
Also, if your stay coincides with a Saturday, take the free Marriott water taxi to the metro station & take the metro to Mo Chit station and enjoy the weekend market there (it's frickin' huge & everything is negotiable!).