For summer camping where you've got electricity- bring along a box fan or cage fan and set it up inside the tent so it sucks air in from the door or window. The breeze and cooler air will help tremendously. Also, I got one of those portable 12/110V refridgerator/warmers from Wal-Mart and bring it with me. I have it plugged into my cigarette lighter on the way to the campsite, and then plug it into the power-strip when I'm at the campsite. It keeps my Yoohoos downright cold If you're going all-out, I suppose you could even get one of those little portable AC units...
I also got a coleman cot from Wal-Mart (hmmm- could there be a trend in my shopping?) that I absolutely love! It actually frees up a lot of room in the tent since you can store your gear under the cot. It's uber-comfy, too.