So many great suggestions here! Our family loves to travel, and we have experienced many wonderul trips. On our must do list for future trips is: Belize (splitting time between the Cayo District in a jungle lodge, and then to Ambergris Caye to enjoy the beach) and an African Safari. I am hoping to do Belize next summer. The Safari...well that may be a pipe dream, but I am going to work on that one and just maybe I can make it a reality! Also, we really want to see Williamsburg. And, a river raft adventure, maybe on the Colorado River, would be cool. Sigh...so much to see and not enough time (or money!)
I agree with others regarding cruising. It is a great way to get a taste of a region, because you get to stop at a number of ports. Also, the majority of ships cater to families, so there are always great options to entertain the little ones and the adults. Also, it is a safe and convenient way to travel.
One trip/experience I will highly recommend for families, is a week at a Dude Ranch. They have great ones in Colorado, Montana and Wyoming. Talk about fun! Two summers ago, our family spent a week at the Paradise Guest Ranch in Buffalo, Wyoming. We drove through South Dakota, and stopped at the Badlands (great hiking!) and the Black Hills along the way. Our DS, who was 9 at the time, made great friends with other kids at the ranch. Our whole family enjoyed riding horses, fly fishing and hiking. The ranch we picked had (about) 60 guests, so we really got to know other families. We met wonderful people from England, Canada, Texas, etc. At the end of the week, the kids put on a rodeo for the parents: barrel racing, key hole, etc. We will never forget that trip!
Happy travels!