As you noticed there are many things you can do. Some more cost effective than others.
Check out the options, consider your situation and skills to determine what works for you.
Many good suggestions already made so will not repeat many of them.

Vent the attic with sufficient air, the goal is to keep as close to outside temp as possible.
Even with good venting the HOT roof radiates heat down to the house.
Reflective radiant films above the insulation is more or as effective as a second roof with ventilation.
Wind induced ventilation can do a great job without requiring power, even with low winds.
A cool attic is more cost effective then more insulation.

Whole house fans are effective only if the evening air temperature drops low enough to make use of it.
If the evening air temperature is low enough then store the "cool" in a thermo mass, maybe eliminating AC run time.

Fans
Fan power is a cubic function, twice the air flow 8 times the power. Air foil shaped blades improve air flow 26% or more, in cubic functions this is half the power. Ceiling fans, air blowers, while house fans use less power with air foil blades. Slow moving air for a long time will use less total power than a high speed fan running for a short time.

Ground Water cooling, if your ground source water is below 60 deg then use it to cool house not AC. Discharge water can be used for watering the lawn or to fill a pond.

ICE block cooling, freeze a large block of ICE in the winter, use to cool Fridge and AC for house.
My home in MI needs 15 foot cube of ICE. Bury it in the ground.

Keep sun off AC condenser.
Keep sun out of home.
Consider pure water misting on AC condenser.
Desiccant to reduce humidity, assuming 60% humidity half the energy to cool is the latent heat of condensing the humidity out. Use AC condenser heat to dry desiccant.

Ground source heat pump.

As mentioned www.builditsolar.com has many inexpensive cooling ideas.