Keep the front door closed: This is a big one in my house. If we keep the front door open, the sun shines straight through the glass storm door and makes the entry area feel like a greenhouse. We notice a dramatic drop in temperature when we keep the front door closed.
Close the blinds/drapes: The same thought process applies to blinds and drapes. Keeping the summer sun out of your home as much as possible means your AC will have to work less to keep the home cool.
Use ceiling fans/exhaust fans: Ceiling fans do a great job of helping you feel comfortable in a particular room. Just remember to turn the ceiling fan off when no one is using that room. In addition, using an exhaust fan in the bathroom and/or kitchen helps get hot air out of those particular areas.