I'm Intrested in finding out if e.g. Earths gravity is calculated with corrections relating to the spin rate of our planet or any other world. If so does this mean gravity would be less on the equator compared to a reading taken at the poles

Yes, the value for 'g' does in fact vary with location on the earth's surface - not just due to the earth's rotation as you suggest but it also varies due to (a) the earth not being perfectly spherical, (b) your altitude - you weigh less at the top of a mountain than in Death Valley, and (c) the density of material in the ground nearby (iron ore is denser than water, for example).

All of these factors are quite small, but can be measured with sensitive enough instruments. In fact geologists use fluctuations in the 'g' to help map the location of certain ores.

Gravity has nothing to do with spin, just with mass. So if the Earth were perfectly flat and round, and made of the same material everywhere, then gravity would be exactly the same everywhere on its surface.

Since it's none of those things, it changes.

NASA has a satellite that shows what those changes are, and you can see the mission details at NASA - At 10, GRACE Continues Defying, and Defining, Gravity (http://www.nasa.gov/mission_pages/Grace/news/grace20120316.html).

There's an iPhone app for this as well, called NASA Now, which shows the gravity maps, but you can see an example image here:

http://www.cosmosmagazine.com/files/imagecache/feature/files/20071020_earth.jpg