There are no scaled maps available for Bangkok - military secret, you see. i found the best maps to be Nancy Chandler maps. Lots of information on the map giving you an idea of relative distances so that you can plan what you want to see in one day and what should be left for another day.
Fondest memory: None of the maps contain much beyond the core area of the city - the airport will not be on any of them, for example, but if you are where most other tourists are, they will do fine. Getting outside of that area gets a bit more adventerous and, depending on your point of view, either less or more interesting.
If you are arriving at the Bangkok International Airport (Don Muang - BKK) don't forget to pick the "Official map of bangkok" ....which is free.
Fondest memory: Best Map in town!