Here's a table of the added yields you get from resources:
Code:
Resource Bonus Improvement
Bananas F FF-P* (Plantation)
Deer F F (Camp)
Sheep F F (Pasture)
Cattle F P (Pasture)
Wheat F F/FF (Farm)
Fish FF GG (Boats)
Horses P P (Pasture)
Oil P P (Well)
Iron P P (Mine)
Aluminum P PP (Mine)
Coal P PP (Mine)
Uranium P PP (Mine)
Whales FG G (Boats)
Pearls GG G (Boats)
Ivory GG G (Camp)
Furs GG G (Camp)
Cotton GG G (Plantation)
Dyes GG G (Plantation)
Incense GG G (Plantation)
Silk GG G (Plantation)
Spices GG G (Plantation)
Wine GG G (Plantation)
Sugar GG FG (Plantation)
Marble GG PG (Quarry)
Gold GG PG (Mine)
Silver GG PG (Mine)
Gems GGG PG (Mine)
* Bananas are treated specially: you get Plains when you cut down the Jungle to build a Plantation, but once the Plantation exists it reverts back to being like Jungle, so Bananas + Plantation is 3 food, 0 production.
As a city always gets a minimum of 2 food, 2 production, 1 gold it doesn't make much sense to settle on a resource tile which gives you less than any of these, unless you need the resource really quickly.
However if you have an abundance of good tiles, and a tile with a resource is either in a great spot for a city, or otherwise so poor you wouldn't work it anyway, building a city there might be a good idea. An example for the latter would be Cotton on a desert tile. If you settle there you get an extra gold in your city tile, which may serve you better than a hex that gives you three gold with plantation but nothing else.