Katie,
I also have the problem you are faced with. My wife and I have a 4 year old that weighs in at 48 pounds. The stroller we have decided to go with is made by Baby Jogger and supports up to 75 lbs. It features an awesome one handed fold feature and folds VERY compact, all you have to do is grab the handle and lift up and voila, it closes on its own. It isnt a cheap stroller but is one that will outlast all the other joggers on the market. It is even roomier than the regular Baby Jogger and fit our needs perfect. The stroller is called the City-Roo and we got ours from A Safer World for Children, they have a toll free number, 1-866-787-1077. One other feature on this stroller is that the front wheels swivel so it can be used anywhere without having steering problems that are normally associated with joggers. I hope this helps.
Kevin