Unless you live in a tremendously humid climate, whole house fans work very well. They're inexpensive compared to central air and they cost just a few dollars a month to run. Also, have a professional check your roof vents to make sure they are sufficient, and add a few if necessary. (This made a HUGE difference in our house!) Install and use ceiling fans. If you have a two story house with a bedroom(s) over the garage, insulate the garage walls. To manage heat, install lined curtains and keep them drawn during the hottest part of the day. Optimize your landscaping to shade the house from the hot southern/western sun. On a daily basis, avoid the oven and plan to eat summer salads that don't require cooking.

Open all the windows (and run whole house fan) at night or when the temp is higher inside than inside and keep the windows closed and curtains pulled the rest of the time. Make it part of you morning and evening routine.
Plant shade trees.
Use ceiling fans, particularly over bed.
When days are unusually hot just stay in the coolest room, go to the library, the mall or to a friend's house.
Cutting a ridge vent in our roof dramatically improved the temp inside the attic and the upper floor. We live in Southern NJ and run the AC only a few hours per year ( it's bc my husband cannot sleep if the air in too humid).

To add to the above suggestions, we also use a couple of these: http://www.amazon.com/gp/product/B00008XET9/ref=oss_product

Watch the price though, it changes quite a bit. We paid around $18/each and they are worth every penny. Work great in a kitchen too that doesn't have an exhaust fan.

We live on the 3rd floor of a building and don't use an air conditioner at all. We have a ceiling fan in the living room and a couple box fans strategically placed in windows for the few weeks when it's unbearably hot, but other than that the best thing is to just open up ALL the windows. The result is a cool and breezy home that feels great 95% of the time. Make sure you open window on all sides so you can get great cross ventilation. Also, make sure to pull down the shades when the hot afternoon sun starts to come in.
And I agree with Sloutre, if you really feel like you're suffering just go to a movie, mix up some margaritas or go to a lake for a swim!

To add to the suggestion above to plan on eating raw foods to avoid turning on the oven - we bought a toaster oven and during the summer use it for *everything* that we want to eat hot. That and the wok, which doesn't need a lot of stove time to serve it's purpose.

Other than that, we just play the "which window is the sun hitting" game all day. Close our east-facing bedroom drapes first thing in the morning, close up the windows when it starts to warm up. Then when our inside thermometer says it's as hot as the outside, we open the doors and windows and put the fans there to make a breeze. We set up a network of tower fans in the halls to pull air from the cool side of the house to hot side, and place the final fan blowing the hot air OUT a window.

My aunt lived in an old house without any isolation. In summer in the early morning she opened all windows to let fresh and cool air into the house. Then she shut the windows and all outside shutters. Even on the hottest days inside her house it was always cool and dark.

It seems to be essential to block the sun from hitting the window panes already. To have shutters on the outside of the windows will be much more efficient than pulling tight the curtains inside the house.

I prefer the combination of closed outside shutters with the slats not being fully closed (if possible) plus all windows open for cross ventilation. This way you'll have a nice filtered light in the house and a gentle breeze. I think, that's how they do it in southern countries.

In Barcelona I've seen curtains on the outside of patio and balcony doors, often hanging over and fixed to the railings like this http://www.pitopia.de/scripts/pictures/detail.php?pid=152015&view=1.

I have also had lots of success with the windows open at night and closed and curtained or shuttered during the day routine.
It works best if you are really vigilant about the timing and have a good outdoor thermometer. Make sure you get the windows open and fans on as soon as it is cooler out than in and make sure you get up and close the windows early enough in the morning that the sun hasn't started heating things back up again. Remember that on the really hot days that will be at sunrise.
There are some houses this won't work very well in but give it a try.

I second the idea of keeping the windows open at night and closed (and dark, thanks to curtains or shutters) during the day. I've lived through summers in Israel with very little air conditioning this way!

All of the above plus, hang some of that foil coated bubble wrap in every window that gets sun. The flatter against the pane the better. I just hang it inside my venetian blinds.

Oh, one other tip: here in Israel, we paint apartment building roofs white in the summer and black in the winter. If it's possible to change the color of your roof, that's a great way to go. (Obviously this is easier with a flat cement roof than paper!)

Hey, I'm in DC, too. We do have central air, but because our house faces east-west, it stays pretty cool. Last year we used the AC for a total of about a week. We open as many windows as possible, use a ceiling fan in the bedroom and table fans otherwise, and we have a terrific whole house fan that makes a HUGE difference (unlike an attic fan, a whole house fan is installed in the ceiling of the second floor and essentially pulls in the outside air -- esp at night, when it's cool outside, it's great).

And yeah, sometimes we sweat a little :)

here's some reasons i will always give up and turn on the ac:

#1 - the midwest. summers in st louis are miserable. when you walk outside in august it's like having a hot, wet blanket wrapped around you. disgusting. just walking outside causes you to be drenched in sweat

#2 - i can't sleep when i'm sweating. even with a ceiling fan ... if it's blowing humid hot air i'm still miserable

#3 - perhaps the biggest reason ... i live in the city, on a first floor apt, alone. there is no way i would leave the windows open while i sleep OR when i leave for the day. regardless of how cool this made my apt, i'd never be comfortable thinking that someone could get in while i'm sleeping. call me paranoid nut, but that's not a risk i'm willing to take.

All the suggestions are good, but why not put awnings over your windows to create an area of shade outside the window? Also, if you have concrete paths under your windows, change the surface to something soft, like wood chips which won't reflect the heat into the house. If such paths have proper footing they won't turn to puddles in winter.

I live in Brazil and we have a hard summer - hot, hot and hot. Even here in São Paulo things can get pretty hard on some days. We don't have AC here in my place - in fact, most houses do not have AC. It leaves the air very dry and hard to breathe ... What we do here in our house is to use a water cooling fan with cold water inside. It helps a lot.

I live in the deep South. I have no air conditioning. I find that if I close my windows on the very first hot summer day, run the ceiling fans 24/7 and not open the windows until fall, my home stays cool. Yes, people complain when they visit, but I just suggest that perhaps it would be better if I came to them for subsequent visits.

We put this up in our sunroom - we love the view in that room but was unbearable in the summer. The windowfilm plus timely use of blinds has made a difference.
http://www.homedepot.com/webapp/catalog/servlet/ContentView?pn=SF_HF_KH_Window_Films&storeId=10051&langId=-1&catalogId=10053