This combination of cheats could possibly the most fun you'l ever have play GTA San Andreas
First, to set the mood, u'l want the Rainy/Storm cheat:
R2, X, L1, L1, L2, L2, L2, Circle
Then, in no particular order, Invisible Cars, Flying Cars and Cars Drive on Water:
Triangle, L1, Triangle, R2, Square, L1, L1
Right, R2, Circle, R1, L2, Square, R1, R2
Square, Down, L2, Up, L1, Circle, Up, X, Left
Now, for the fun part, spawn the Rhino:
Circle, Circle, L1, Circle, Circle, Circle, L1, L2, R1, Triangle, Circle, Triangle
And there you have it! Your pretty much indestructable in the rhino, you can fly over area 53 and not have them shoot at you and to land just hold the brake and point your nose towards the ground. This also works divebombing the water, just don't do it from a very big height because uyou will get stuck just underneath the surface and won't be able to go up or down, or get out.
You also have to be a little careful because you can't get out of any car while flying or on the water, and the Rhino tends to tip backwards after a couple shots in a row while flying and you'l fall.
Other than that, your golden!
Have fun!!!