An attic "exhaust" type fan blows the hot air out of your attic. It does help keep your house a bit cooler, and it also prolongs the life of your roof. This is something you set and forget -- literally, its up there and you dont do anything to it. I'm surprised you don't already have one, they are typically part of a roof installation. If you dont' already have one, I'm not sure I'd put one in now if you are anywhere close to getting a new roof. If you are a couple of years away from a new roof then I'd wait, do some research, and pick a lighter colored shingle too. They are generally installed by roofers, as they involve cutting a hole in the outside of your roof and flashing around the fan. If you do this, we had some roof work done by Showalter roofing once and would recommend them. We have a home that was built in 1975 that we have lived in for 8 years. The upstairs was always much hotter than the downstairs, sometimes unbearably so. We had a lot of new insulation blown into the attic and it no longer feels like the ceiling of the 2nd floor is part of an oven, and insulation isnt' that expensive compared to other things you can do. We have something called "trol a temp" -- it is a damper system, which is so-so. In theory, the two termostats, one for upstairs, one for downstairs, work together, to direct the cold air upstairs. The trick is to set the upstairs to a colder temp and the downstairs to a warmer temp which is also warmer than the temp the downstairs currently is. If the downstairs heats up enough to trigger the A/C for the downstairs, the dampers switch back to directing the air to the downstairs. For some reason, my husband doesn't understand this, (even after 8 years) and I can wake up sweating to walk downstairs to a freezing kitchen. He will then tell me that he was hot, so he lowered the temp on the thermostat DOWNSTAIRS which was completely the wrong thing to do. It gets annoying to keep going upstairs to fiddle w/ the thermostat. A true 2 zone system means a seperate A/C unit that serves only the 2nd story of your home. This of course will work the best and also cost the most.
As a kid, we had a "whole house fan" which is sometimes also called an "attic fan." This is basically an alternative to A/C. If you are running a whole house fan you don't air conditioning on too. For the whole house fan, you have a big fan mounted into the side of your house up high (inside is probably in your attic.) Then on the second floor, maybe in the upstairs hallway, there will be a second door or hatch to open when you have the fan on. You open all the windows, turn on the fan, and the fan is very powerful and pulls air in through the open windows. It creates a nice breeze and does cool things off, especially at night. One thought I have though is I grew up on the East Coast, and even though we had plenty of hot days, the nights were always cooler than they are here. In the midwest, it seems like once it gets hot, it stays hot. This will never be better than air conditioning though, so I'd look at some of the other choices.