I would like ocean surface temperature data for locations along the US
ocean coasts. At least one data point for each state, and several for
Florida & California would be good. If possible a map would be the
most helpful.

I would also like a temperature map of daily highs, lows, and mean
temperature for each month for the same regions as the Ocean data.
Again, I would strongly prefer a map if one is available.

Now for the weather questions:
1. Does the surface temperature of ocean coasts usually vary greatly
through the day, or is it as I suspect fairly stable?

2. I would also like to know if the transition from highs to lows is
generally the same curve from one place to another. If so, what is the
curve shape? I'd imagine it is a sine-wave design?

Noaa would have that deep in their records. They measure it by
satellite.  http://www.noaa.gov/ocean.html

dalman, thanks for the link. They do have data tables which are very
useful. I would bet the air temperatures won't be too difficult to
find myself.

Try this link at noaa - it gives a great graphic for clicking on
bouys.  On the Chesapeake Bay where I run a charter boat the water
temperature will rise and fall up to 4 degrees or so during the day. 
You'll see that the ocean bouys generally record less of a change. 
Some show erratic data because the ocean is more susceptible to
upwelling and currents that change temperature.  As a side note, Air
temperature (convection)has less to do with water temperature change
than the amount of daylight and the angle of the sun (solar
radiation).  Also in the ocean the Gulf Stream is a large factor in
water temperatures.

Forgot the link - http://www.ndbc.noaa.gov/

Very good link. Thanks!