Lets see a lots been covered already.
For lifting heavy engines, transmissions or tractors - Chain hoist and a floor jack, axle stands are handy as well.
The new battery powered LED trouble lights are way better and safer than the old 120volt type. I can never seem to get the light where I want it with a corded light.
A press is really handy for removing and installing bearings. Saves a lot of pounding and cussing.
An electrolysis tank - a 45gallon plastic drum makes a good sized one and isn't expensive.
A warm dry place to work with lots of light.
Tool storage. A good tool box on wheels is a real help for keeping things organized.