My most recent overheating problem was my fan wires/connector. Does your fan come on 100% of the time? If not, ground the fan to the battery to see if the fan is any good.
My other overheating problems and how I fixed them were:
* Fan relays in PCM/CCRM went bad.
I replaced the module and it was good to go. (~$200)
* Heater core was leaking.
I used Bar's Stop Leak and the problem went away, and has been gone for about 2 years now. (~$10, 15 minutes)
* Thermostat went bad.
I replaced the thermostat. I recommend a 180° thermostat if you live in a hot area (~$8, 2 minutes)
* Coolant Temperature Sensor broke.
I replaced the sensor and all was good. (~$35)
Other problems could be:
* Radiator cap is bad.
Replace the radiator cap.
* Radiator gets really dirty and crappy, inside and out, causing circulation and heat exchange to be poor.
Replace the radiator.
* Fan cycles are not kicking in when they are supposed to.
Check the fan, and then all sensors and relays that trigger it.
* Coolant mix is incorrect.
Adjust accordingly by adding either water or coolant.
* Air in the lines.
Burp the system. Easiest way to fill the system with coolant is by jacking up the nose of the car and adding coolant until it takes no more.
* Head gasket is bad and is leaking exhaust fumes and gases into the coolant, thus raising temperatures.
Replace the head gasket.
* Water pump is bad. The fins can get dirty and reduce water circulation.
Replace the water pump.