Summer Heat
Living in Florida, where we get the hottest temputers and the coldest of the whole state. We range from 90-110 in the summer, and with the humidity the heat index is usually around 130. I am happy to say I have never ever lost a rabbit to heat stroke. And here is how:

I have a giant fan in the rabbit shed, and on hot days I put it on high. It is loud and blows really hard, the rabbits enjoy the movement in air it gives though, and they never even reacted to the noise. I also freeze old cokebottles with water, and give it to them to lay up agaisnt and lick when it's really hot. They usually don't freeze over night after I use them, so I have to keep a couple extra ones for the ones that aren't frozen. Last year I had about 30 rabbits, and used 60 bottles just to keep everyone cool all the time. This year I'll probably have to have even more.
Anyway this is what I do in the summer when it's really hot. Also my shed has tarps on it for walls, and we open them up so air can circulate through the shed. Sometimes I take the water hose and water the roof to cool it down.

Winter Freeze
In the winter I must go through about 5-6 bails of hay. When it gets down below freezing, I give everyone enough hay to lay in to keep them off the cold cage floor. This has seemed to work very well for me. We close the tarp walls every year at about November, because that's when the Floridian winter starts. They stay closed till about March or April, to keep all the heat in from during the day. I have to clean the old nasty hay out from the cages at about every 2 days to keep them from laying in their own waste. I give them new hay and clean out the whole shed at the end of every winter.
This may take alot of time, but I haven't lost nearly as much as my fellow breeders have. Also those of you who live where it goes below zero, I would say to bring them inside over night in carriers, just to be safe. I know alot of people have space heaters, but I would rather be safe then sorry.

Heat Stroke

A rabbit who has heat stroke will die if they are not cooled down quickly. But if you cool them down too quickly they could go into shock.

   In the early stages of heat stroke, the rabbit will lay in its cage, stretched out, breathing heavy. They will often tilt their up upward and breath heavy. I have also noticed that rabbits in heavy heat will sweat from around the nose, and it almost looks like snuffles, but it's not.
As heat stroke gets worse, they will become lazy and unresponsive. Sometimes they will turn blue around the nose. When this happens, they are very close to death.

Treatment of Heat Stroke

Take the rabbit inside, or somewhere cool immediatly. Give him water with ice in it. Crush the ice if you can and try to put some of the ice water up to his mouth and bathe his ears and face in it. Don't get it up his nose though or he may become sick later on.

If this still doesn't work, fill up the sink and place him in room temputure water for a couple of seconds. Take him out and dry him off as best as you can. Try to keep the ears cool. The ears to a rabbit is like our foreheads when we have a temputure. If they are really hot, the rabbit is probably hot.

If this still doesn't work, your rabbit maybe dehydrated and will need to see a vet. If you waste time trying to use some of these steps when they are clearly not working, the rabbits life will slip away. For pet owners who are not experienced with animals, I would say to wet a towel, wrap the rabbit in it, bring it ice and water to drink on the way, and rush as soon as possible to the vet.